Add keyboard shortcuts

Add keyboard shortcuts to <describe the app>. The most common actions
are: <list them>

- Follow conventions people already know. Don't reassign Ctrl+S,
  Ctrl+F or Escape to something surprising.
- Never fire while the user is typing in an input, unless it's a
  modifier combination.
- A discoverable list — "?" opens a shortcuts panel — and hints on
  the buttons themselves.
- Escape closes whatever is open, always.
- Work on both platforms: Cmd on Mac, Ctrl elsewhere.

Then tell me which of my actions genuinely deserve a shortcut and
which would just be clutter.