docs: add music discovery, autoplay, and Mumble admin sections

- USAGE.md: music discovery (!similar, !tags), autoplay discovery
  config, Mumble admin (!mu) command reference
- CHEATSHEET.md: music discovery and Mumble admin quick reference
- ROADMAP.md: mark v2.4.0 as done, add MB fallback + !mu + autoplay
- TODO.md: mark music discovery and performance items as done
- PROJECT.md: update plugin categories table
- TASKS.md: close open doc items

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

PROJECT.md

@@ -28,10 +28,13 @@ CLI (argparse) -> Config (TOML) -> Bot (orchestrator)
 | Category | Plugins | Purpose |
 |----------|---------|---------|
 | Core | core | Bot management, help, plugin lifecycle |
-| OSINT | dns, crtsh | Reconnaissance and enumeration |
+| OSINT | dns, crtsh, internetdb | Reconnaissance and enumeration |
 | Red Team | revshell, encode, hash | Offensive tooling |
 | OPSEC | defang | Safe IOC handling |
-| Utility | cidr, example | Network tools, demo |
+| Utility | cidr, rand, timer, remind | Network tools, scheduling |
+| Music | music, lastfm | Mumble playback, discovery (Last.fm/MB) |
+| Voice | voice, mumble_admin | STT/TTS, server admin |
+| Subscriptions | rss, yt, twitch, alert | Feed monitoring, keyword alerts |
 
 ### Key Design Decisions