feat: voice profiles, rubberband FX, per-bot plugin filtering

- Add rubberband package to container for pitch-shifting FX
- Split FX chain: rubberband CLI for pitch, ffmpeg for filters
- Configurable voice profile (voice, fx, piper params) in [voice]
- Extra bots inherit voice config (minus trigger) for own TTS
- Greeting is voice-only, spoken directly by the greeting bot
- Per-bot only_plugins/except_plugins filtering on Mumble
- Alias plugin, core plugin tests

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

Containerfile

@@ -1,6 +1,6 @@
 FROM python:3.13-alpine
 
-RUN apk add --no-cache opus ffmpeg yt-dlp && \
+RUN apk add --no-cache opus ffmpeg yt-dlp rubberband && \
     ln -s /usr/lib/libopus.so.0 /usr/lib/libopus.so
 
 WORKDIR /app