A history of every action, with undo and redo

The feedback log is append-only. Add a history page (all events, newest first, per piece), undo (appends the inverse event, so the log stays complete) and redo. Show the last action in the device bar with an "undo" link.

Done when: feedback/history.html exists, undo and redo work offline, and "Copy for Claude" carries undone events marked as such.