Renaming a board can be undone: renameBoard logs the row it overwrote #59

renameBoard now runs inside a transaction and calls logAction, just like every other mutation, so it's trimmed by MAX_UNDO_DEPTH and shows up in the undo log like anything else.

Payload gained restoreBoardName?: { id: string; name: string }, and undo restores only the name — not the whole board row — so undoing a rename can never revert a claimBoard. renameBoard now returns boolean (false for an unknown board id, doing nothing) instead of void; the one caller in routes.ts already validates the board first, so this doesn't change route behavior.

Added three tests to src/db.test.ts:

• move a card, rename the board, undo → old name back, card untouched; a second undo then reverses the move.
• renaming a nonexistent board returns false and logs nothing.
• an action row written in the old shape (no restoreBoardName) still undoes cleanly.

bun test is green (113 pass). Left untouched per the issue: static/board.*.js and src/pages/board.ts — no client-side label or button changes here.

Closes #42