docs: update docs for Mumble integration

Add Mumble sections to USAGE.md, CHEATSHEET.md, API.md, README.md.
Mark Mumble done in ROADMAP.md and TODO.md. Update TASKS.md sprint.

TODO.md

@@ -105,6 +105,61 @@ is preserved in git history for reference.
 - [ ] Markdown/HTML formatting mode toggle
 - [ ] Webhook mode (for setWebhook instead of getUpdates)
 
+## Discord
+
+- [ ] Discord adapter via WebSocket gateway + REST API (no SDK)
+- [ ] DiscordBot + DiscordMessage (duck-typed with IRC Message)
+- [ ] Gateway intents for message content
+- [ ] Message splitting at 2000-char limit
+- [ ] Permission tiers via user/role IDs
+- [ ] Slash command registration (optional)
+
+## Matrix
+
+- [ ] Matrix adapter via long-poll `/sync` endpoint (no SDK)
+- [ ] MatrixBot + MatrixMessage (duck-typed with IRC Message)
+- [ ] Room-based messaging (rooms map to channels)
+- [ ] Power levels map to permission tiers
+- [ ] E2EE support (optional, requires libolm)
+
+## XMPP
+
+- [ ] XMPP adapter via persistent TCP + XML stanzas (no SDK)
+- [ ] XMPPBot + XMPPMessage (duck-typed with IRC Message)
+- [ ] MUC (Multi-User Chat) support -- rooms map to channels
+- [ ] SASL authentication
+- [ ] TLS/STARTTLS connection
+
+## Mumble
+
+- [x] Mumble adapter via TCP/TLS + protobuf control channel (no SDK)
+- [x] MumbleBot + MumbleMessage (duck-typed with IRC Message)
+- [x] Text chat only (no voice)
+- [x] Channel-based messaging
+- [x] Minimal protobuf encoder/decoder (no protobuf dep)
+
+## Slack
+
+- [ ] Slack adapter via Socket Mode WebSocket (no SDK)
+- [ ] SlackBot + SlackMessage (duck-typed with IRC Message)
+- [ ] OAuth token + WebSocket for events
+- [ ] Channel/DM messaging
+- [ ] Permission tiers via user IDs
+
+## Mattermost
+
+- [ ] Mattermost adapter via WebSocket API (no SDK)
+- [ ] MattermostBot + MattermostMessage (duck-typed with IRC Message)
+- [ ] Self-hosted Slack alternative
+- [ ] Channel/DM messaging
+
+## Bluesky
+
+- [ ] Bluesky adapter via AT Protocol firehose + REST API (no SDK)
+- [ ] BlueskyBot + BlueskyMessage (duck-typed with IRC Message)
+- [ ] Mention-based command dispatch
+- [ ] Post/reply via `com.atproto.repo.createRecord`
+
 ## Testing
 
 - [x] Plugin command unit tests (encode, hash, dns, cidr, defang)