feat: add TTS voice guidance during GPS-tracked workouts

Voice announcements run entirely in the Android foreground service
(works with screen locked). Configurable via web UI before starting
GPS: time-based or distance-based intervals, selectable metrics
(total time, distance, avg/split/current pace), language (en/de).

Also syncs workout pause/resume state to the native service — pausing
the workout timer now freezes the Android-side elapsed time, distance
accumulation, and TTS triggers.

Includes TTS engine detection with install prompt if none found, and
Android 11+ package visibility query for TTS service discovery.

src-tauri/gen/android/app/src/main/AndroidManifest.xml

@@ -11,6 +11,12 @@
     <!-- AndroidTV support -->
     <uses-feature android:name="android.software.leanback" android:required="false" />
 
+    <queries>
+        <intent>
+            <action android:name="android.intent.action.TTS_SERVICE" />
+        </intent>
+    </queries>
+
     <application
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"