Pass 2 collab polish — Discord setup UI and workspace CRUD
Campaign owners can configure Discord webhooks from the board header, test pings before going live, and manage campaigns/boards with rename and delete flows.
- Discord bridge panel: paste webhook URL, toggle DM whispers, save, and send a test ping — no API-only setup.
- Sidebar CRUD: new campaign/board creation, rename via prompt, delete with confirmation (boards guarded when last in campaign).
- Session casting circle: spell-only drop feedback, undo-last stub, and cast flash when a spell lands in the play zone.
Impact: Remote tables can wire Discord in one sitting, and DMs can reset workspace clutter without database access.