Add location-aware automatic default bounding box

The OpenSky "Default bounding box" now follows where flying happens.
A new "Automatic" picker mode (the default) resolves the live-map area
from a location cascade — drone telemetry → phone GPS → browser
geolocation → the user's Region country → Europe — instead of a fixed
box. Manual presets and Custom coordinates still work.

- Web App: new shared countries.js dataset (all countries + bbox,
  offline point→country); the bbox picker gains all European countries
  and an Automatic option (client pref prefs.autoBbox); the Region
  setting expands from 6 locale entries to all countries; the live map
  resolves the cascade each poll and sends it as ?bbox=.
- API Server: the states endpoint accepts and validates a ?bbox=
  override (validBBox); the Web App BFF forwards the query; the hub
  relays new phoneLatitude/phoneLongitude telemetry to the Web App.
- Fly App: reports the phone's own GPS (geolocator) alongside
  telemetry, used as the "your location" fallback.
- API panel: the OpenSky bbox picker lists all European countries.

Builds verified across web, panel, both Go modules and the Fly App
APK. Region list, Automatic default and the cascade ?bbox= override
verified in the browser.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Fly App/lib/flight_model.dart

@@ -21,6 +21,10 @@ class FlightModel extends ChangeNotifier {
   double? altitude;
   double? latitude;
   double? longitude;
+  // Phone's own GPS (independent of the drone's fix above); streamed to the
+  // server as a location fallback for the Web App's automatic bounding box.
+  double? phoneLatitude;
+  double? phoneLongitude;
   int? batteryPercent;
 
   UploadStatus upload = UploadStatus.disabled;