feat(block2): 'use my location' — set the sharing area without typing a code

Makes the coarse area human, per feedback that a typed code is jargon.
- CoarseLocationProvider interface + geolocator-backed impl (BSD-3): low
  accuracy only, returns null on any denial/error (degrades quietly). Behind an
  interface so it's fakeable and the plugin stays at the composition root.
- Config sheet: a 'Use my approximate location' button (shown only when a
  provider is wired) fills the area from the device position, reduced to a
  5-char geohash via commons_core's Geohash — a precise fix never leaves the
  device. 'Couldn't get your location' on failure.
- Threaded via TaneApp(location); main wires GeolocatorCoarseLocation.
- Platform: ACCESS_COARSE_LOCATION (Android) + NSLocationWhenInUseUsageDescription
  (iOS), both scoped to the coarse-area use.
- i18n en/es/pt. Widget test fills the area from a fake location. 8 tests green.

apps/app_seeds/pubspec.yaml

@@ -62,6 +62,10 @@ dependencies:
   material_symbols_icons: ^4.2951.0
   url_launcher: ^6.3.2
   package_info_plus: ^9.0.1
+  # Optional coarse device location (BSD-3) to set the sharing area without
+  # typing a code. Low accuracy only; the value is immediately reduced to a
+  # low-precision geohash. Behind an interface so it's fakeable and pluggable.
+  geolocator: ^13.0.1
 
 dev_dependencies:
   flutter_test: