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

src-tauri/src/lib.rs

@@ -0,0 +1,11 @@
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+    tauri::Builder::default()
+        .plugin(tauri_plugin_http::init())
+        .plugin(tauri_plugin_store::Builder::new().build())
+        .plugin(tauri_plugin_notification::init())
+        .plugin(tauri_plugin_clipboard_manager::init())
+        .plugin(tauri_plugin_dialog::init())
+        .run(tauri::generate_context!())
+        .expect("error while running tauri application");
+}