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

electron/preload.ts

@@ -14,7 +14,7 @@ import {
   type WindowMode
 } from '../shared/ipc';
 import type { EveFlowBridge, Unsubscribe } from '../shared/bridge';
-import { VOICE_IPC, type SynthesizeRequest, type SynthesizeResult, type TranscribeRequest, type TranscribeResult, type VoiceDownloadProgress, type VoiceEngineStatus, type VoiceModelStatus } from '../shared/voice';
+import { VOICE_IPC, type KwsDetection, type KwsStartRequest, type SynthesizeRequest, type SynthesizeResult, type TranscribeRequest, type TranscribeResult, type VoiceDownloadProgress, type VoiceEngineStatus, type VoiceModelStatus } from '../shared/voice';
 
 function subscribe<T>(channel: string, callback: (payload: T) => void): Unsubscribe {
   const listener = (_event: Electron.IpcRendererEvent, payload: T) => callback(payload);
@@ -69,7 +69,11 @@ const api: EveFlowBridge = {
     onProgress: (cb: (progress: VoiceDownloadProgress) => void) => subscribe<VoiceDownloadProgress>(VOICE_IPC.modelsProgress, cb),
     transcribe: (req: TranscribeRequest) => ipcRenderer.invoke(VOICE_IPC.transcribe, req) as Promise<TranscribeResult>,
     synthesize: (req: SynthesizeRequest) => ipcRenderer.invoke(VOICE_IPC.synthesize, req) as Promise<SynthesizeResult>,
-    unload: (id?: string) => ipcRenderer.invoke(VOICE_IPC.unload, id) as Promise<unknown>
+    unload: (id?: string) => ipcRenderer.invoke(VOICE_IPC.unload, id) as Promise<unknown>,
+    kwsStart: (req: KwsStartRequest) => ipcRenderer.invoke(VOICE_IPC.kwsStart, req) as Promise<{ accepted: string[]; rejected: string[] }>,
+    kwsStop: () => ipcRenderer.invoke(VOICE_IPC.kwsStop) as Promise<void>,
+    kwsAudio: (pcm: Uint8Array, sampleRate: number) => ipcRenderer.send(VOICE_IPC.kwsAudio, pcm, sampleRate),
+    onKwsDetected: (cb: (detection: KwsDetection) => void) => subscribe<KwsDetection>(VOICE_IPC.kwsDetected, cb)
   }
 };