feat: playlist save/load, queue durations, whisper bias, greet fix

- Move TTS greeting from mumble._play_greet to voice.on_connected
  (fires once on first connect, gated on _is_audio_ready)
- Add initial_prompt multipart field to Whisper STT for trigger word
  bias (auto-generated from trigger config, overridable)
- Enhanced !queue: elapsed/total on now-playing, per-track durations,
  footer with track count and total time
- New !playlist command: save/load/list/del named playlists via
  bot.state persistence (playlist:<name> keys)
- Fix duck floor test (1% -> 2% to match default change)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_music.py

@@ -956,7 +956,7 @@ class TestDuckCommand:
         msg = _Msg(text="!duck")
         asyncio.run(_mod.cmd_duck(bot, msg))
         assert any("Duck:" in r for r in bot.replied)
-        assert any("floor=1%" in r for r in bot.replied)
+        assert any("floor=2%" in r for r in bot.replied)
         assert any("restore=30s" in r for r in bot.replied)
 
     def test_toggle_on(self):