Channel.x_type enum(general|work|report|discuss|triage|custom); required
and validated on channel creation (400 if missing/invalid).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
- new channel_members table; creator always added, plus selected members
- Channel.isPublic (default false): public channels visible to all guild
members; non-public only to explicit members
- GET /channels filters to channels visible to the requesting user
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>