Separate 'Clear' (reset key) from 'Delete' (remove shortcut)

Today handleClearKey at App.jsx:833 removes the assignment entirely (per memory feedback_release_retag_procedure: "must delete both :: and ::double entries"). Add a true reset path: "Clear key" wipes the key combo but keeps the action payload (so the shortcut shows in the list as draft, ready for re-recording). Rename current "Clear" → "Delete". Both actions exposed in the context menu.