Merge feat/server-batched-vad: faster-whisper batched + VAD (spec 001 workstream 5)

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

# Conflicts:
#	docs/Decisions.md

docs/WorkBreakdown.md

@@ -153,6 +153,9 @@ Notes (M4):
       (CTranslate2) via a Python sidecar in `server-py/`, spawned/supervised by
       Bun (D-013 supersedes the Transformers.js-under-Bun plan); map the shared
       model catalog to faster-whisper model ids in `src/lib/models.ts`
+- [x] Batched inference + tuned Silero VAD for server-engine file
+      transcriptions, live passes sequential (spec 001 Goal 5, D-WS5a):
+      ≈ 2× faster on CPU int8 at equal-or-better WER; segments ≤ 30 s chunks
 - [x] Degrade gracefully when Python/the sidecar is absent (server engine
       unavailable; browser engine untouched — anonymous path deploys with Bun alone)
 - [x] `POST /api/transcribe` — auth-guarded, streamed JSON-lines response (D-011),