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/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "agent-ui"
+version = "0.1.0"
+description = "Agent UI - Desktop & Mobile App"
+authors = ["you"]
+edition = "2021"
+
+[lib]
+name = "agent_ui_lib"
+crate-type = ["staticlib", "cdylib", "rlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+tauri-plugin-http = "2"
+tauri-plugin-store = "2"
+tauri-plugin-notification = "2"
+tauri-plugin-clipboard-manager = "2"
+tauri-plugin-dialog = "2"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"