Move settings gear to header right (next to identity) on all pages.
Add history clock button in header left that opens a new slide-out
history panel with Activity feed and Time Machine tabs. Embed author
identity (DID, username, timestamp) in Automerge change messages via
JSON envelope, with backward-compatible parsing for old plain strings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
