Download sidecar on first launch instead of bundling

Major refactor: sidecar is no longer bundled in the installer. Instead,
it's downloaded on first launch with a setup screen offering CPU vs CUDA
choice. This solves the 2GB+ installer size limit and decouples app/sidecar.

Backend:
- New commands: check_sidecar, download_sidecar, check_sidecar_update
- Streaming download with progress events via reqwest
- Added reqwest + futures-util dependencies
- Removed sidecar.zip from bundle resources
- Restored NSIS target (no longer size-constrained)

CI:
- Each platform builds both CPU and CUDA sidecar variants (except macOS: CPU only)
- Sidecar zips uploaded as separate release assets
- Asset naming: sidecar-{os}-{arch}-{variant}.zip

Frontend:
- SidecarSetup.svelte: first-launch setup with CPU/CUDA radio choice,
  progress bar, error/retry handling
- Update banner on launch if newer sidecar version available
- Conditional rendering: setup screen → main app flow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/components/SidecarSetup.svelte

@@ -0,0 +1,320 @@
+<script lang="ts">
+  import { invoke } from '@tauri-apps/api/core';
+  import { listen } from '@tauri-apps/api/event';
+  import type { UnlistenFn } from '@tauri-apps/api/event';
+  import { onMount } from 'svelte';
+
+  interface Props {
+    onComplete: () => void;
+  }
+
+  let { onComplete }: Props = $props();
+
+  let variant = $state<'cpu' | 'cuda'>('cpu');
+  let downloading = $state(false);
+  let downloadProgress = $state({ downloaded: 0, total: 0, percent: 0 });
+  let error = $state('');
+  let success = $state(false);
+
+  let unlisten: UnlistenFn | null = null;
+
+  onMount(() => {
+    return () => {
+      unlisten?.();
+    };
+  });
+
+  function formatBytes(bytes: number): string {
+    if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(0)} KB`;
+    if (bytes < 1024 * 1024 * 1024) return `${(bytes / (1024 * 1024)).toFixed(0)} MB`;
+    return `${(bytes / (1024 * 1024 * 1024)).toFixed(1)} GB`;
+  }
+
+  async function startDownload() {
+    downloading = true;
+    error = '';
+    success = false;
+
+    unlisten = await listen<{ downloaded: number; total: number; percent: number }>(
+      'sidecar-download-progress',
+      (event) => {
+        downloadProgress = event.payload;
+      }
+    );
+
+    try {
+      await invoke('download_sidecar', { variant });
+      success = true;
+      // Brief pause so the user sees "Complete" before the screen goes away
+      setTimeout(() => {
+        onComplete();
+      }, 800);
+    } catch (err) {
+      error = String(err);
+    } finally {
+      downloading = false;
+      unlisten?.();
+      unlisten = null;
+    }
+  }
+</script>
+
+<div class="setup-overlay">
+  <div class="setup-card">
+    <h1 class="app-title">Voice to Notes</h1>
+    <h2 class="setup-heading">First-Time Setup</h2>
+    <p class="setup-description">
+      Voice to Notes needs to download its AI engine to transcribe audio.
+    </p>
+
+    {#if !downloading && !success}
+      <div class="variant-options">
+        <label class="variant-option" class:selected={variant === 'cpu'}>
+          <input type="radio" name="variant" value="cpu" bind:group={variant} />
+          <div class="variant-info">
+            <span class="variant-label">Standard (CPU)</span>
+            <span class="variant-desc">Works on all computers (~500 MB download)</span>
+          </div>
+        </label>
+        <label class="variant-option" class:selected={variant === 'cuda'}>
+          <input type="radio" name="variant" value="cuda" bind:group={variant} />
+          <div class="variant-info">
+            <span class="variant-label">GPU Accelerated (CUDA)</span>
+            <span class="variant-desc">Faster transcription with NVIDIA GPU (~2 GB download)</span>
+          </div>
+        </label>
+      </div>
+
+      {#if error}
+        <div class="error-box">
+          <p class="error-text">{error}</p>
+          <button class="btn-retry" onclick={startDownload}>Retry</button>
+        </div>
+      {:else}
+        <button class="btn-download" onclick={startDownload}>
+          Download &amp; Install
+        </button>
+      {/if}
+    {:else if downloading}
+      <div class="progress-section">
+        <div class="progress-bar-track">
+          <div class="progress-bar-fill" style="width: {downloadProgress.percent}%"></div>
+        </div>
+        <p class="progress-text">
+          {downloadProgress.percent}% — {formatBytes(downloadProgress.downloaded)} / {formatBytes(downloadProgress.total)}
+        </p>
+        <p class="progress-hint">Downloading {variant === 'cuda' ? 'GPU' : 'CPU'} engine...</p>
+      </div>
+    {:else if success}
+      <div class="success-section">
+        <div class="success-icon">&#10003;</div>
+        <p class="success-text">Setup complete!</p>
+      </div>
+    {/if}
+  </div>
+</div>
+
+<style>
+  .setup-overlay {
+    position: fixed;
+    inset: 0;
+    background: #0a0a23;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 10000;
+  }
+
+  .setup-card {
+    background: #16213e;
+    border: 1px solid #2a3a5e;
+    border-radius: 12px;
+    padding: 2.5rem 3rem;
+    max-width: 480px;
+    width: 90vw;
+    color: #e0e0e0;
+    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.5);
+    text-align: center;
+  }
+
+  .app-title {
+    font-size: 1.8rem;
+    margin: 0 0 0.25rem;
+    color: #e94560;
+    font-weight: 700;
+  }
+
+  .setup-heading {
+    font-size: 1.1rem;
+    margin: 0 0 0.75rem;
+    color: #e0e0e0;
+    font-weight: 500;
+  }
+
+  .setup-description {
+    font-size: 0.9rem;
+    color: #b0b0b0;
+    margin: 0 0 1.5rem;
+    line-height: 1.5;
+  }
+
+  .variant-options {
+    display: flex;
+    flex-direction: column;
+    gap: 0.75rem;
+    margin-bottom: 1.5rem;
+    text-align: left;
+  }
+
+  .variant-option {
+    display: flex;
+    align-items: flex-start;
+    gap: 0.75rem;
+    padding: 0.85rem 1rem;
+    border: 1px solid #2a3a5e;
+    border-radius: 8px;
+    cursor: pointer;
+    transition: border-color 0.15s, background 0.15s;
+  }
+
+  .variant-option:hover {
+    border-color: #4a5568;
+    background: rgba(255, 255, 255, 0.02);
+  }
+
+  .variant-option.selected {
+    border-color: #e94560;
+    background: rgba(233, 69, 96, 0.08);
+  }
+
+  .variant-option input[type='radio'] {
+    margin-top: 0.2rem;
+    accent-color: #e94560;
+    flex-shrink: 0;
+  }
+
+  .variant-info {
+    display: flex;
+    flex-direction: column;
+    gap: 0.2rem;
+  }
+
+  .variant-label {
+    font-size: 0.9rem;
+    font-weight: 500;
+    color: #e0e0e0;
+  }
+
+  .variant-desc {
+    font-size: 0.78rem;
+    color: #888;
+  }
+
+  .btn-download {
+    background: #e94560;
+    border: none;
+    color: white;
+    padding: 0.7rem 1.5rem;
+    border-radius: 6px;
+    cursor: pointer;
+    font-size: 0.9rem;
+    font-weight: 500;
+    width: 100%;
+    transition: background 0.15s;
+  }
+
+  .btn-download:hover {
+    background: #d63851;
+  }
+
+  .progress-section {
+    margin-top: 0.5rem;
+  }
+
+  .progress-bar-track {
+    width: 100%;
+    height: 8px;
+    background: #1a1a2e;
+    border-radius: 4px;
+    overflow: hidden;
+    border: 1px solid #2a3a5e;
+  }
+
+  .progress-bar-fill {
+    height: 100%;
+    background: #e94560;
+    border-radius: 4px;
+    transition: width 0.3s ease;
+  }
+
+  .progress-text {
+    margin: 0.75rem 0 0;
+    font-size: 0.85rem;
+    color: #e0e0e0;
+    font-variant-numeric: tabular-nums;
+  }
+
+  .progress-hint {
+    margin: 0.35rem 0 0;
+    font-size: 0.78rem;
+    color: #888;
+  }
+
+  .error-box {
+    background: rgba(233, 69, 96, 0.1);
+    border: 1px solid rgba(233, 69, 96, 0.3);
+    border-radius: 8px;
+    padding: 1rem;
+  }
+
+  .error-text {
+    color: #e94560;
+    font-size: 0.85rem;
+    margin: 0 0 0.75rem;
+    word-break: break-word;
+    line-height: 1.4;
+  }
+
+  .btn-retry {
+    background: #e94560;
+    border: none;
+    color: white;
+    padding: 0.5rem 1.25rem;
+    border-radius: 6px;
+    cursor: pointer;
+    font-size: 0.85rem;
+    font-weight: 500;
+  }
+
+  .btn-retry:hover {
+    background: #d63851;
+  }
+
+  .success-section {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 0.5rem;
+    padding: 1rem 0;
+  }
+
+  .success-icon {
+    width: 48px;
+    height: 48px;
+    border-radius: 50%;
+    background: rgba(78, 205, 196, 0.15);
+    color: #4ecdc4;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 1.5rem;
+    font-weight: 700;
+  }
+
+  .success-text {
+    color: #4ecdc4;
+    font-size: 1rem;
+    margin: 0;
+    font-weight: 500;
+  }
+</style>

src/routes/+page.svelte

@@ -8,6 +8,7 @@
   import AIChatPanel from '$lib/components/AIChatPanel.svelte';
   import ProgressOverlay from '$lib/components/ProgressOverlay.svelte';
   import SettingsModal from '$lib/components/SettingsModal.svelte';
+  import SidecarSetup from '$lib/components/SidecarSetup.svelte';
   import { segments, speakers } from '$lib/stores/transcript';
   import { settings, loadSettings } from '$lib/stores/settings';
   import type { Segment, Speaker } from '$lib/types/transcript';
@@ -18,13 +19,56 @@
   let audioUrl = $state('');
   let showSettings = $state(false);
 
+  // Sidecar state
+  let sidecarReady = $state(false);
+  let sidecarChecked = $state(false);
+
+  // Sidecar update state
+  let sidecarUpdate = $state<{ current_version: string; latest_version: string } | null>(null);
+  let showUpdateDownload = $state(false);
+  let updateDismissed = $state(false);
+
   // Project management state
   let currentProjectPath = $state<string | null>(null);
   let currentProjectName = $state('');
   let audioFilePath = $state('');
 
+  async function checkSidecar() {
+    try {
+      const ready = await invoke<boolean>('check_sidecar');
+      sidecarReady = ready;
+    } catch {
+      sidecarReady = false;
+    }
+    sidecarChecked = true;
+  }
+
+  async function checkSidecarUpdate() {
+    try {
+      const update = await invoke<{ current_version: string; latest_version: string } | null>('check_sidecar_update');
+      sidecarUpdate = update;
+    } catch {
+      // Silently ignore update check failures
+    }
+  }
+
+  function handleSidecarSetupComplete() {
+    sidecarReady = true;
+    checkSidecarUpdate();
+  }
+
+  function handleUpdateComplete() {
+    showUpdateDownload = false;
+    sidecarUpdate = null;
+  }
+
   onMount(() => {
     loadSettings();
+    checkSidecar().then(() => {
+      if (sidecarReady) {
+        checkSidecarUpdate();
+      }
+    });
 
     // Global keyboard shortcuts
     function handleKeyDown(e: KeyboardEvent) {
@@ -443,14 +487,31 @@
   }
 </script>
 
-{#if !appReady}
+{#if !appReady || !sidecarChecked}
   <div class="splash-screen">
     <h1 class="splash-title">Voice to Notes</h1>
     <p class="splash-subtitle">Loading...</p>
     <div class="splash-spinner"></div>
   </div>
+{:else if sidecarChecked && !sidecarReady && !showUpdateDownload}
+  <SidecarSetup onComplete={handleSidecarSetupComplete} />
+{:else if showUpdateDownload}
+  <SidecarSetup onComplete={handleUpdateComplete} />
 {:else}
   <div class="app-shell">
+  {#if sidecarUpdate && !updateDismissed}
+    <div class="update-banner">
+      <span class="update-text">
+        Sidecar update available (v{sidecarUpdate.current_version} &rarr; v{sidecarUpdate.latest_version})
+      </span>
+      <button class="update-btn" onclick={() => showUpdateDownload = true}>
+        Update
+      </button>
+      <button class="update-dismiss" onclick={() => updateDismissed = true} title="Dismiss">
+        &times;
+      </button>
+    </div>
+  {/if}
   <div class="app-header">
     <div class="header-actions">
       <button class="settings-btn" onclick={openProject} disabled={isTranscribing}>
@@ -674,4 +735,45 @@
   @keyframes spin {
     to { transform: rotate(360deg); }
   }
+
+  /* Sidecar update banner */
+  .update-banner {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 0.5rem 1rem;
+    background: rgba(78, 205, 196, 0.1);
+    border-bottom: 1px solid rgba(78, 205, 196, 0.25);
+    color: #e0e0e0;
+    font-size: 0.85rem;
+  }
+  .update-text {
+    flex: 1;
+    color: #b0b0b0;
+  }
+  .update-btn {
+    background: #4ecdc4;
+    border: none;
+    color: #0a0a23;
+    padding: 0.3rem 0.85rem;
+    border-radius: 4px;
+    cursor: pointer;
+    font-size: 0.8rem;
+    font-weight: 600;
+  }
+  .update-btn:hover {
+    background: #3dbdb5;
+  }
+  .update-dismiss {
+    background: none;
+    border: none;
+    color: #888;
+    font-size: 1.1rem;
+    cursor: pointer;
+    padding: 0.1rem 0.3rem;
+    line-height: 1;
+  }
+  .update-dismiss:hover {
+    color: #e0e0e0;
+  }
 </style>