Wake hal for wallet-connect requests while it is closed

Step 3, first half. Android Chrome freezes backgrounded PWAs and closes their
relay sockets, so a phone with hal "open" answers nothing — which is what made
Amethyst spin. Push is the only way to reach a frozen app.

- service worker gains a `push` handler. It deliberately does NOT spend: if a
  window is open it nudges it to re-listen, otherwise it raises a notification
  that opens hal on tap. Putting a spend path in the worker is the remaining
  half and wants its own testing.
- hal-side: request permission, subscribe with the notifier's VAPID key, and
  register its service pubkeys with nwcpush.coinos.io. Turning it off
  deregisters, unsubscribes, and clears the pouch — no reason to leave
  spendable keys where a worker can read them if nothing will.
- a Settings toggle, and the ark feature exposes the ASP context the pouch
  record needs.

Co-Authored-By: Claude Fable 5 <[email protected]>

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