feat(gateway): split video recording into silence-based segments like voice

Video (camera + screen share) DAVE stream-watch now produces per-burst
MP4 segments instead of one long .h264 per watch:
- Detects VIDEO_SILENCE_MS (4000ms) of no H264 packets → closes the
  current segment, muxes to MP4, registers in voice_recordings + uploads
  to TeleUploader, then reopens for the next burst (mirrors voice AfterSilence).
- Per-watch segment counter + per-segment depacketizer reset + closing
  guard + write-error swallow so races (silence close vs in-flight UDP
  packet) never corrupt files or crash the gateway.
- Frontend: recordings deck renders a native <video> player for MP4 rows
  (detected by filename), keeps single-playback registry across audio+video.

.hermes/plans/2026-09-01_video-recording-splitting.md

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+# Video Recording Splitting — Like Voice Recording
+
+## Goal
+Camera + screen share (stream watch) recording should split into per-burst
+segments just like voice recording does — each time a streamer pauses/stops
+and resumes, a new MP4 segment is created and registered in the DB + uploaded.
+
+## Voice Recording Model (to replicate)
+1. `receiver.speaking.start` → new OGG segment per burst
+2. AfterSilence (4000ms) → stream "end" → segment finalized + uploaded
+3. Each segment → DB insert → OGG→MP3 transcode → upload → update DB
+4. File stored as `<userId>/<startTime>.ogg` + `.json`
+
+## Video Recording Splitting
+1. DAVE video RTP → depacketize H264 → write to current segment .h264
+2. Silence detection: no H264 packets for 4000ms → close segment → flush →
+   mux to MP4 → insert DB record → upload → start new segment on next packet
+3. Each segment: `<userId>/video-<channelId>-<startTime>.h264` → `.mp4`
+4. DB: reuse `voice_recordings` table (filename indicates video, e.g. `video-XXX-1234.mp4`)
+5. Upload: MP4 to TeleUploader (no transcode needed — MP4 plays everywhere)
+
+## Files Modified
+- `services/discord-gateway/src/modules/voice-recording/streamWatchReceiver.ts`
+  — Main change: silence-based splitting + DB registration + upload
+
+## Constants
+- `VIDEO_SILENCE_MS = 4000` (matches voice AfterSilence)
+- `VIDEO_MIN_SEGMENT_MS = 1000` (skip segments <1s — avoid noise)
+
+## Verification
+- `pnpm typecheck` in `services/discord-gateway`
+- `pnpm build` (dist/ is the deployed artifact)
+- Push → CI deploy → live test with a streamer