Record the batched-VAD measurements and check heartbeat, bursts and cancel against the real sidecar

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/Architecture.md

@@ -204,7 +204,9 @@ environment). See `WorkBreakdown.md` for the itemized checklist.)
    (`server-py/`) that Bun spawns and supervises (D-013; faster-whisper has no
    browser/WASM build, so it is server-only — the browser stays on Transformers.js).
    `src/server/transcribe.ts` bridges the sidecar's segment stream to the streamed
-   JSON-lines HTTP response (D-011). The shared catalog maps model ids to
+   JSON-lines HTTP response (D-011). File requests (`mode: "file"`) decode with
+   faster-whisper's batched pipeline over Silero-VAD speech chunks; server-live
+   passes send `mode: "live"` and stay sequential (D-WS5a). The shared catalog maps model ids to
    `Systran/faster-whisper-*` CTranslate2 conversions. If the sidecar is absent,
    the server engine reports unavailable; the browser/anonymous flow is unaffected.
 4. Both engines implement the same `Engine` interface in `src/lib/engine.ts`, so the