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>

docs/USAGE.md

@@ -1760,6 +1760,53 @@ file (natural dedup).
   missing (e.g. after a cleanup or volume mount issue)
 - On cancel/error, files are not deleted (needed for `!resume`)
 
+### Music Discovery
+
+Find similar music and genre tags for artists. Uses Last.fm when an API
+key is configured; falls back to MusicBrainz automatically (no key
+required).
+
+```
+!similar              Similar to currently playing track
+!similar <artist>     Similar artists to named artist
+!similar play         Queue a random similar track
+!similar play <artist> Queue a similar track for named artist
+!tags                 Genre tags for currently playing artist
+!tags <artist>        Genre tags for named artist
+```
+
+- When an API key is set, Last.fm is tried first for richer results
+- When no API key is set (or Last.fm returns empty), MusicBrainz is
+  used as a fallback (artist search -> tags -> similar recordings)
+- `!similar play` picks a random result and delegates to `!play`
+  (searches YouTube for the artist + title)
+- MusicBrainz rate limit: 1 request/second (handled automatically)
+
+Configuration (optional):
+
+```toml
+[lastfm]
+api_key = ""          # Last.fm API key (or set LASTFM_API_KEY env var)
+```
+
+### Autoplay Discovery
+
+During autoplay, the bot periodically discovers new tracks instead of
+only playing from the kept library. Every Nth autoplay pick (configurable
+via `discover_ratio`), it queries Last.fm or MusicBrainz for a track
+similar to the last-played one. Discovered tracks are searched on YouTube
+and queued automatically.
+
+Configuration (optional):
+
+```toml
+[music]
+autoplay = true           # Enable autoplay (default: true)
+autoplay_cooldown = 30    # Seconds between autoplay tracks (default: 30)
+discover = true           # Enable discovery during autoplay (default: true)
+discover_ratio = 3        # Discover every Nth pick (default: 3)
+```
+
 ### Extra Mumble Bots
 
 Run additional bot identities on the same Mumble server. Each extra bot
@@ -1856,3 +1903,24 @@ Available voices:
 
 To switch the active voice, set `piper_tts_voice` (e.g.
 `fr_FR-siwis-medium`) and redeploy the TTS service.
+
+### Mumble Server Admin (admin)
+
+Manage Mumble users and channels via chat commands. All subcommands
+require admin tier. Mumble-only (no-op on other adapters).
+
+```
+!mu kick <user> [reason]     Kick user from server
+!mu ban <user> [reason]      Ban user from server
+!mu mute <user>              Server-mute user
+!mu unmute <user>            Remove server-mute
+!mu deafen <user>            Server-deafen user
+!mu undeafen <user>          Remove server-deafen
+!mu move <user> <channel>    Move user to channel
+!mu users                    List connected users
+!mu channels                 List server channels
+!mu mkchan <name> [parent]   Create channel (under parent or root)
+!mu rmchan <name>            Remove empty channel
+!mu rename <old> <new>       Rename channel
+!mu desc <channel> <text>    Set channel description
+```