feat: integrate Tauri v2 with Android widget and voice assistant

- Add Tauri v2 shell (Cargo, tauri.conf.json, capabilities, plugins)
- Migrate all fetch() calls to apiFetch() for Tauri-aware HTTP
- Migrate WebSocket endpoints to resolveEndpoints() for dynamic URLs
- Add ServerConfigDialog for remote server URL configuration
- Add tauri.ts lib with isTauri detection, apiFetch wrapper, plugin helpers
- Add server-config Pinia store with persistence via plugin-store
- Conditional PWA (disabled in Tauri builds)
- Android: home screen transcript widget (last 5 messages, 30s refresh)
- Android: voice command / share activity (SpeechRecognizer + WebSocket)
- Android: signed release APK with auto-copy to installers/
- Remove stale frontend/src-tauri directory

frontend/vite.config.ts

@@ -6,7 +6,10 @@ import path from 'path'
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url))
 
+const isTauri = !!process.env.TAURI_ENV_PLATFORM
+
 export default defineConfig({
+  envPrefix: ['VITE_', 'TAURI_ENV_'],
   resolve: {
     alias: {
       '@': path.resolve(__dirname, 'src'),
@@ -16,7 +19,8 @@ export default defineConfig({
   },
   plugins: [
     vue(),
-    VitePWA({
+    // PWA only in web builds (not Tauri)
+    ...(!isTauri ? [VitePWA({
       registerType: 'autoUpdate',
       includeAssets: ['favicon.svg', 'icons/*.svg', 'icons/*.png'],
       devOptions: {
@@ -67,7 +71,7 @@ export default defineConfig({
           }
         ]
       }
-    })
+    })] : [])
   ],
   server: {
     port: 4100,