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

shared/bridge.ts

@@ -12,6 +12,8 @@ import type {
   WindowMode
 } from './ipc';
 import type {
+  KwsDetection,
+  KwsStartRequest,
   SynthesizeRequest,
   SynthesizeResult,
   TranscribeRequest,
@@ -72,5 +74,10 @@ export interface EveFlowBridge {
     transcribe: (req: TranscribeRequest) => Promise<TranscribeResult>;
     synthesize: (req: SynthesizeRequest) => Promise<SynthesizeResult>;
     unload: (id?: string) => Promise<unknown>;
+    kwsStart: (req: KwsStartRequest) => Promise<{ accepted: string[]; rejected: string[] }>;
+    kwsStop: () => Promise<void>;
+    /** Fire-and-forget 16-bit PCM frames for the keyword spotter. */
+    kwsAudio: (pcm: Uint8Array, sampleRate: number) => void;
+    onKwsDetected: (cb: (detection: KwsDetection) => void) => Unsubscribe;
   };
 }