The iOS app's icon count, pushed by ipx (#433)

Background refresh runs when iOS chooses, and for this app that has
been rarely, so the icon's unread count lagged until the app was
opened (#421). Now ipx sends the count:
- ipx: a push_devices table and POST/DELETE /api/push/devices. With
  [push] set to an APNs key, a task compares each phone's All
  Subscriptions unread count with the last sent, once a minute, and
  sends a changed one to Apple as a badge-only push: no alert, no
  sound. A token Apple says is gone is forgotten. The signing token is
  ES256 over the team and time, made again every forty minutes, inside
  Apple's limits.
- iOS: the aps-environment entitlement. The app registers for push
  once badge permission is given, each launch, and hands its token to
  the page.
- Page: registers the token with ipx as the person signed in, since
  the player's address (ipxapi) lets through only the player's paths,
  and removes it on signing out.

jsonwebtoken here is built without PEM support, so the .p8 key's
base64 is decoded in push.rs rather than turning on a feature and
changing Cargo.lock for one file.

cargo test -p ipx on macOS: 182 pass; the 3 that fail read /proc and
fail there without this change too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- In the iOS app, the page registers the phone with ipx for its icon's count, and signing out removes it (#433).
 - In the iOS app, the icon's unread count follows the page's: reading and new items change it at once, not the next time the app is opened (#421).
 - In the iOS app, presses are felt: play, pause, flag, pull to refresh, marking read and errors each give the phone's haptic for it (#430).
 - A sleep timer in the player: 5 minutes to an hour, then playback fades out and pauses. In the iOS app the phone keeps the time, so it works with the screen locked; the app and Safari also get an AirPlay button. On a phone the title has the player's top line to itself, with the controls either side of play below it (#429).