Add Hocuspocus and Yjs collaborative notes example

[sdairs]

Two editors can share three plain-text notes, make concurrent insertions/deletions and reconnect after offline edits. Hocuspocus/Yjs synchronize the original CRDT state; a row-locked PostgreSQL binary merge preserves history when snapshots arrive late or repeat. The UI distinguishes peer synchronization from an actual post-commit snapshot receipt and reports storage failure honestly.

Includes a React/CodeMirror client, restricted owner/runtime grants, explicit CA/name verification, Origin/token/document controls, bounded protocol/state/SQL work, reproducible setup and a scoped build/unit workflow. Single trusted local workspace and one server process; no per-user accounts or horizontal live coordination.

Validation: native Linux ARM64 clean locked install, production build, three unit tests and formatting pass; six real Cloud storage/role/TLS controls pass, including competing row locks and deferred COMMIT rollback. Two separate Chromium processes converge through concurrent edits, deletion and offline/reconnect. Actual delayed/failed storage preserves prior committed data and reports its status; a later successful edit recovers. The original process exits before replacement, which loads exact committed binary/revision/time and fresh-browser text. WebSocket origin, token, document and payload negatives pass. Reviewed disposable Cloud fixture deleted; VM preserved. Companion article remains local for publication review.