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>

package.json

@@ -0,0 +1,27 @@
+{
+  "name": "local-transcription",
+  "private": true,
+  "version": "1.4.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite dev",
+    "build": "vite build",
+    "preview": "vite preview",
+    "tauri": "tauri"
+  },
+  "devDependencies": {
+    "@sveltejs/vite-plugin-svelte": "^5.0.0",
+    "@tauri-apps/cli": "^2.0.0",
+    "@tsconfig/svelte": "^5.0.0",
+    "svelte": "^5.0.0",
+    "svelte-check": "^4.0.0",
+    "typescript": "~5.6.0",
+    "vite": "^6.0.0"
+  },
+  "dependencies": {
+    "@tauri-apps/api": "^2.0.0",
+    "@tauri-apps/plugin-dialog": "^2.0.0",
+    "@tauri-apps/plugin-shell": "^2.0.0",
+    "@tauri-apps/plugin-process": "^2.0.0"
+  }
+}