- TopBar: call closeBoard() before navigating back to prevent data loss
- board-store: guard debouncedSave against race condition when board is
closed during an in-flight save
- board-store: add missing updatedAt to setColumnWidth
- useKeyboardShortcuts: remove duplicate Ctrl+K handler that prevented
command palette from toggling closed
- AttachmentSection: wire up Tauri file dialog for adding attachments
with link/copy mode support