Add Tauri v2 + Svelte 5 frontend and headless Python backend

Scaffold the cross-platform rewrite from PySide6/Qt to Tauri + Svelte,
following the same architecture as voice-to-notes. The Python backend
runs headless as a sidecar, with a FastAPI control API that the Svelte
frontend connects to via REST and WebSocket.

New files:
- backend/app_controller.py: Headless orchestration (extracted from MainWindow)
- backend/api_server.py: FastAPI control endpoints + /ws/control WebSocket
- backend/main_headless.py: Headless entry point for sidecar mode
- src-tauri/: Tauri v2 Rust shell with sidecar and dialog plugins
- src/: Svelte 5 frontend (App, Settings, Controls, TranscriptionDisplay)
- src/lib/stores/: Reactive stores for backend connection, config, transcriptions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "local-transcription"
+version = "1.4.0"
+description = "Real-time speech-to-text transcription for streamers"
+authors = ["Local Transcription Contributors"]
+edition = "2021"
+
+[lib]
+name = "local_transcription_lib"
+crate-type = ["lib", "cdylib", "staticlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+tauri-plugin-shell = "2"
+tauri-plugin-dialog = "2"
+tauri-plugin-process = "2"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"

src-tauri/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    tauri_build::build()
+}

src-tauri/gen/schemas/capabilities.json

@@ -0,0 +1 @@
+{}

src-tauri/src/lib.rs

@@ -0,0 +1,9 @@
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+    tauri::Builder::default()
+        .plugin(tauri_plugin_shell::init())
+        .plugin(tauri_plugin_dialog::init())
+        .plugin(tauri_plugin_process::init())
+        .run(tauri::generate_context!())
+        .expect("error while running tauri application");
+}

src-tauri/src/main.rs

@@ -0,0 +1,6 @@
+// Prevents additional console window on Windows in release
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
+
+fn main() {
+    local_transcription_lib::run()
+}

src-tauri/tauri.conf.json

@@ -0,0 +1,42 @@
+{
+  "productName": "Local Transcription",
+  "version": "1.4.0",
+  "identifier": "com.localtranscription.app",
+  "build": {
+    "frontendDist": "../dist",
+    "devUrl": "http://localhost:1420",
+    "beforeDevCommand": "npm run dev",
+    "beforeBuildCommand": "npm run build"
+  },
+  "app": {
+    "windows": [
+      {
+        "title": "Local Transcription",
+        "width": 800,
+        "height": 600,
+        "minWidth": 640,
+        "minHeight": 480,
+        "resizable": true
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.ico",
+      "icons/icon.png"
+    ]
+  },
+  "plugins": {
+    "shell": {
+      "open": true
+    }
+  }
+}