feat(tts): add native local iOS TTS (AVSpeechSynthesizer) (#4697)

Implement on-device iOS text-to-speech using AVSpeechSynthesizer,
mirroring the Android native TextToSpeech plugin so the shared
NativeTTSClient drives both platforms through the same command and
tts_events contract.

- Swift NativeTTSPlugin: speak/stop/pause/resume/rate/pitch/voice and
  voice enumeration, with region-disambiguated duplicate voice names and
  a small preUtteranceDelay to avoid first-word clipping.
- Enable the native TTS client on iOS in TTSController.
- Make TTS teardown resilient: reset UI state up front and tear down the
  controller, media session, and background audio in parallel so a slow
  native shutdown can never leave the TTS icon or lock-screen session
  stuck on.
- Keep iOS on navigator.mediaSession for the lock screen (Android uses
  the native foreground service), which restores the Edge TTS cover and
  current-sentence metadata.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/readest-app/src/app/reader/hooks/useTTSControl.ts

@@ -535,26 +535,42 @@ export const useTTSControl = ({ bookKey, onRequestHidePanel }: UseTTSControlProp
   const handleStop = useCallback(
     async (bookKey: string) => {
       const ttsController = ttsControllerRef.current;
-      if (ttsController) {
-        await ttsController.shutdown();
-        ttsControllerRef.current = null;
-        setTtsController(null);
-        getView(bookKey)?.deselect();
-        setIsPlaying(false);
-        emitPlaybackState('stopped');
-        onRequestHidePanel?.();
-        setShowIndicator(false);
-        setShowBackToCurrentTTSLocation(false);
-      }
+      // Reset all UI/session state up front — including the TTS toggle
+      // (ttsEnabled) and indicator that color the TTS icon — so disabling TTS
+      // always takes effect immediately. The teardown below is best-effort and
+      // must never block or skip these resets if it hangs or throws, which was
+      // observed with iOS system TTS (Edge TTS was unaffected). See #4676.
+      ttsControllerRef.current = null;
+      setTtsController(null);
+      setIsPlaying(false);
+      emitPlaybackState('stopped');
+      onRequestHidePanel?.();
+      setShowIndicator(false);
+      setShowBackToCurrentTTSLocation(false);
       previousSectionLabelRef.current = undefined;
-      if (appService?.isIOSApp) {
-        await invokeUseBackgroundAudio({ enabled: false });
-      }
+      setTTSEnabled(bookKey, false);
+      getView(bookKey)?.deselect();
       if (appService?.isMobile) {
         releaseUnblockAudio();
       }
-      await deinitMediaSession();
-      setTTSEnabled(bookKey, false);
+
+      // Tear down the controller, the lock-screen media session, and the
+      // background-audio session best-effort and IN PARALLEL. The controller's
+      // own shutdown can stall on iOS system TTS, and it must NOT gate the media
+      // session / background-audio teardown — otherwise the lock-screen Now
+      // Playing keeps running after TTS is disabled (Edge TTS was unaffected
+      // because it never hits the stalling native path). See #4676.
+      await Promise.all([
+        ttsController
+          ? Promise.resolve()
+              .then(() => ttsController.shutdown())
+              .catch((error) => console.warn('TTS shutdown failed:', error))
+          : Promise.resolve(),
+        appService?.isIOSApp
+          ? invokeUseBackgroundAudio({ enabled: false }).catch(() => {})
+          : Promise.resolve(),
+        deinitMediaSession().catch(() => {}),
+      ]);
     },
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [appService],