Kanban: a shared CRDT document

One live.doc, zero RPC handlers. A cards map plus one order array per column; every edit applies to the local replica in the same tick and merges everywhere. Concurrent moves from two tabs both survive (per-element CRDT identity), and offline edits reconcile in one exchange on reconnect - the local replica IS the offline queue.

Editing as Cosmic Wizard (0fdb311c)