Cloud strategies previously gave no in-editor signal of sync health: pending,
failed, and offline states were invisible until an exit attempt, and OCC
conflicts were pushed to strategyConflictProvider which nothing watched.

Adds CloudSyncStatusChip to the editor top strip (cloud strategies only):
synced / syncing / offline / needs-attention states with 150ms transitions,
a popover explaining each state with last-synced time, and a retry action
that flushes the op queue and media upload queue. Conflict pushes now toast
("your view was updated to the latest version") and are consumed so the
list no longer grows unbounded. convexConnectionProvider exposes the
Convex WebSocket state reactively, seeded to avoid an offline flash.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>