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/voice.ts

@@ -1,7 +1,7 @@
 /** Local voice engine contract (sherpa-onnx in a utility process). Shared by main and renderer. */
 
-export type VoiceModelKind = 'stt' | 'tts';
-export type VoiceEngineKind = 'whisper' | 'sense-voice' | 'nemo-transducer' | 'kokoro' | 'piper';
+export type VoiceModelKind = 'stt' | 'tts' | 'kws';
+export type VoiceEngineKind = 'whisper' | 'sense-voice' | 'nemo-transducer' | 'kokoro' | 'piper' | 'kws-transducer';
 
 export interface VoiceSpeaker {
   id: number;
@@ -69,6 +69,19 @@ export interface SynthesizeResult {
   audioSec: number;
 }
 
+export interface KwsStartRequest {
+  modelId: string;
+  /** Wake phrases in plain text (e.g. "jarvis", "hey jarvis"). */
+  keywords: string[];
+  /** 1 (strict) .. 5 (eager) */
+  sensitivity: number;
+}
+
+export interface KwsDetection {
+  keyword: string;
+  at: number;
+}
+
 export interface VoiceEngineStatus {
   available: boolean;
   error?: string;
@@ -86,5 +99,9 @@ export const VOICE_IPC = {
   modelsProgress: 'voice:models:progress',
   transcribe: 'voice:transcribe',
   synthesize: 'voice:synthesize',
-  unload: 'voice:unload'
+  unload: 'voice:unload',
+  kwsStart: 'voice:kws:start',
+  kwsStop: 'voice:kws:stop',
+  kwsAudio: 'voice:kws:audio',
+  kwsDetected: 'voice:kws:detected'
 } as const;