- bridge between main-process menu events and the command dispatcher
- optional transform: convert raw IPC payload to command args
- extends ipc.ts with ipc.menu.on() helper
- TDD: 5 unit tests covering subscription, payload transform, no-op, unmount
- 'mod+s' / 'mod+shift+s' / 'Tab' / etc.
- mod = meta (Mac) or ctrl (others)
- suppresses when <input>/<textarea>/contentEditable focused
- preventDefault on match
- TDD: 15 unit tests covering parser, match, suppression, unmount