feat: use Edge TTS (Korean Hyunsu voice @ +45%) as the default voice

The user chose Microsoft Edge TTS, voice ko-KR-HyunsuMultilingualNeural at rate
+45% (~1.45x), as the natural Korean voice. Wire it into the bridge and make it
the default engine.

- bridge/server.py: _edge_synthesize() calls edge-tts and transcodes the MP3 to
  PCM16 mono WAV with the system ffmpeg (temp file for a correct header);
  TTS_ENGINE default -> edge; EDGE_TTS_VOICE / EDGE_TTS_RATE env-driven
- requirements-bridge.txt: add edge-tts (lightweight; httpx)
- compose/.env.example/README: TTS_ENGINE=edge + EDGE_TTS_* knobs; note the
  online/privacy trade-off (reply text is sent to Microsoft, needs internet)
- drop the now-unused MeloTTS build layer (Dockerfile) and melo-worker
  (supervisord) — edge synthesises in-process, no model/worker baked, slimmer
  and faster image; settings UI engine list -> edge/piper, restart only bridge

Verified on host: edge-tts -> ffmpeg yields a valid 16-bit mono 24kHz WAV;
envsubst renders tts_engine=edge; docker build --check + 26 tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker-compose.yml

@@ -68,16 +68,13 @@ services:
       WHISPER_COMPUTE_TYPE: ${WHISPER_COMPUTE_TYPE:-float16}
       # TTS engine. Rendered into /app/config/jarvis.json via envsubst (the
       # bridge reads that JSON BEFORE the env, so it must carry the real engine,
-      # not the template's old hardcoded "piper" — otherwise Korean text is read
-      # by the English Piper voice). Default melo; .env can override.
-      TTS_ENGINE: ${TTS_ENGINE:-melo}
-      # MeloTTS on the GPU (cu128 torch baked by docker/setup-melo.sh). CPU synth
-      # serialised under load and pushed TTS to 7-8s; GPU does ~0.3s/sentence.
-      MELO_DEVICE: ${MELO_DEVICE:-cuda}
-      # Speaking rate for MeloTTS. Set here (with a default) so supervisord's
-      # %(ENV_MELO_SPEED)s passthrough always resolves and an .env override
-      # actually reaches the melo-worker. Lower it (e.g. 1.1) for a calmer pace.
-      MELO_SPEED: ${MELO_SPEED:-1.5}
+      # not a hardcoded one — otherwise Korean text is read by the English Piper
+      # voice). Default edge; .env can override (e.g. piper for offline).
+      TTS_ENGINE: ${TTS_ENGINE:-edge}
+      # Edge TTS voice + rate (the chosen natural Korean voice). NOTE: edge is an
+      # ONLINE engine — reply text is sent to Microsoft and needs internet.
+      EDGE_TTS_VOICE: ${EDGE_TTS_VOICE:-ko-KR-HyunsuMultilingualNeural}
+      EDGE_TTS_RATE: ${EDGE_TTS_RATE:-+45%}
       # Optional single-language lock for replies (empty = user's own language).
       OUTPUT_LANGUAGE: ${OUTPUT_LANGUAGE:-ko}
       # Drop the pre-loop planner LLM call to cut voice-reply latency on small