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>

.env.example

@@ -34,18 +34,18 @@ WHISPER_DEVICE=cuda
 WHISPER_COMPUTE_TYPE=float16
 # Optional explicit Piper voice model (.onnx). If empty, the jarvis default is used.
 TTS_PIPER_MODEL_PATH=
-# TTS engine: "melo" (default) uses the MeloTTS Korean voice served by the warm
-# melo-worker (Korean speaker, speed 1.5). Set to "piper" to use Piper directly.
-TTS_ENGINE=melo
-# Melo-only by default: if MeloTTS synthesis fails the bridge returns no audio
-# rather than speaking Korean through the English Piper voice (which mangles it).
-# Set to 1 only if you explicitly want the Piper fallback.
+# TTS engine: "edge" (default) uses Microsoft Edge TTS, a natural Korean neural
+# voice. Set to "piper" for the offline English voice. NOTE: edge is ONLINE —
+# reply text is sent to Microsoft's servers and needs internet.
+TTS_ENGINE=edge
+# Edge voice + speaking rate. Rate is a percentage (+45% ≈ 1.45×). Korean voices:
+# ko-KR-HyunsuMultilingualNeural (M), ko-KR-InJoonNeural (M), ko-KR-SunHiNeural (F).
+EDGE_TTS_VOICE=ko-KR-HyunsuMultilingualNeural
+EDGE_TTS_RATE=+45%
+# Neural-only by default: if synthesis fails the bridge returns no audio rather
+# than speaking Korean through the English Piper voice. Set to 1 to allow the
+# Piper fallback.
 MELO_FALLBACK_PIPER=0
-# Where the bridge reaches the in-container MeloTTS worker, and how long it
-# waits for a synthesis. Speaking rate is set on the worker via MELO_SPEED.
-MELO_WORKER_URL=http://127.0.0.1:8770
-MELO_TIMEOUT=30
-MELO_SPEED=1.5
 
 # ---------------------------------------------------------------------------
 # Jarvis brain (Ollama-backed). In Docker these populate the rendered