feat: add extra Mumble bot instances and TTS greeting

Support [[mumble.extra]] config for additional Mumble identities that
inherit connection settings from the main [mumble] section. Extra bots
get their own state DB and do not run the voice trigger by default.

Add TTS greeting on first connect via mumble.greet config option.
Merlin joins as a second identity with his own client certificate.

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

docs/USAGE.md

@@ -1696,6 +1696,27 @@ file (natural dedup).
 - Use `!kept clear` to delete all preserved files
 - On cancel/error, files are not deleted (needed for `!resume`)
 
+### Extra Mumble Bots
+
+Run additional bot identities on the same Mumble server. Each extra bot
+inherits the main `[mumble]` connection settings and overrides only what
+differs (username, certificates, greeting). Extra bots share the plugin
+registry but get their own state DB and do **not** run the voice trigger
+by default (prevents double-processing).
+
+```toml
+[[mumble.extra]]
+username = "merlin"
+certfile = "secrets/mumble/merlin.crt"
+keyfile = "secrets/mumble/merlin.key"
+greet = "The sorcerer has arrived."
+```
+
+- `username`, `certfile`, `keyfile` -- identity overrides
+- `greet` -- TTS message spoken on first connect (optional)
+- All other `[mumble]` keys (host, port, password, admins, etc.) are inherited
+- Voice trigger is disabled unless the extra entry includes a `voice` key
+
 ### Voice STT/TTS
 
 Transcribe voice from Mumble users via Whisper STT and speak text aloud
@@ -1723,6 +1744,7 @@ TTS behavior:
 - Piper outputs 22050Hz WAV; ffmpeg resamples to 48kHz automatically
 - TTS shares the audio output with music playback
 - Text is limited to 500 characters
+- Set `greet` in `[mumble]` or `[[mumble.extra]]` for automatic TTS on first connect
 
 ### Always-On Trigger Mode