feat: always-on wake word with sherpa-onnx keyword spotting (v2.2.0)

- Catalog: 3.3 MB zipformer keyword-spotting model (kws-en).
- shared/keywords: BPE encoding of wake phrases (SentencePiece table for common words,
  greedy longest-match fallback over the model vocabulary) and keywords file builder.
- Worker: KeywordSpotter stream fed with 16-bit PCM, detections pushed as unsolicited
  messages; engine derives the keywords file, maps sensitivity to threshold/score,
  forwards detections to the renderer and re-arms after a worker restart.
- Renderer: WakeListener keeps one microphone stream, batches 256 ms frames to the
  spotter and captures the command on the same stream after detection (pre-roll, VAD),
  then resumes spotting; the wake word also interrupts speech. Settings: wake mode
  (off / always-on / transcript filter), keyword, sensitivity, status and one-click
  model download; HUD caption shows the active keyword.
- Validated: detection in the worker (fork) and through the real Electron IPC path on
  Kokoro audio, no false positive on an English recording; 23 unit tests.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Wn5VX9HNbJ7N54hR24u9Y

src/App.tsx

@@ -44,6 +44,18 @@ function useBoot(): boolean {
       if (api) {
         disposers.push(useVoiceModels.getState().subscribe());
         void useVoiceModels.getState().refresh();
+        if (settings.voice.wakeMode === 'kws') void voiceController.startWakeMode();
+        let lastWake = JSON.stringify([settings.voice.wakeMode, settings.voice.wakeWord, settings.voice.kwsSensitivity, settings.voice.micDeviceId]);
+        disposers.push(
+          useSettings.subscribe((s) => {
+            const v = s.settings.voice;
+            const key = JSON.stringify([v.wakeMode, v.wakeWord, v.kwsSensitivity, v.micDeviceId]);
+            if (key === lastWake) return;
+            lastWake = key;
+            if (v.wakeMode === 'kws') void voiceController.restartWakeMode();
+            else void voiceController.stopWakeMode();
+          })
+        );
         disposers.push(api.hermes.onPush(handlePush));
         disposers.push(
           api.hotkeys.on((event) => {