[family collaborator] edits on one device appear on the other device

Prove the cross-device guarantees: edits made on device A reach device B over realtime, Y.Text merges char-by-char (not last-write-wins), the IndexedDB replay survives a kill on either device, leader election keeps exactly one tab as the workqueue claimer, lazy WebSocket opens only when needed (no idle ping storms), offline drains preserve op order, presence fans out across devices, kanban drag converges, PDF render works on both device classes, and a brand-new collaborator joining via shared link sees the full workspace state. The read-only link variant proves the planned /view/ read-only surface gates writes.

Proof set for User adds a job on laptop, opens phone — job present immediately