Add Android support with configurable server URL and location permissions

- Add shared_preferences for persisting server URL
- Add SettingsService and PlatformService
- Add server URL input field on non-web platforms
- Make ApiConfig baseUrl configurable at runtime
- Add Android location permissions (ACCESS_FINE/COURSE_LOCATION, INTERNET)
- Request location permission on login and map init
- Fix geo_id type: use String instead of int (UUID format)
- Align share_service with API spec: remove unique_id, use share_id only
- Fix watch endpoint response: last_update instead of created_at
- Add error handling with SnackBars for geo operations
- Wrap login screen in SingleChildScrollView for keyboard handling
- Update map tile layer with userAgentPackageName for OSM

pubspec.yaml

@@ -38,9 +38,12 @@ dependencies:
   cupertino_icons: ^1.0.8
   provider: ^6.1.1
   http: ^1.2.0
+  crypto: ^3.0.3
+  convert: ^3.1.1
   flutter_map: ^6.1.0
   latlong2: ^0.9.1
   geolocator: ^14.0.2
+  shared_preferences: ^2.2.2
 
 dev_dependencies:
   flutter_test:
@@ -57,7 +60,6 @@ dev_dependencies:
 # following page: https://dart.dev/tools/pub/pubspec
 
 # The following section is specific to Flutter packages.
-  args: any
 flutter:
   generate: true