halkyon_app: data locations as precise as a country or a state

An operator's DATA_LOCATION and BACKUP_LOCATION may name a subdivision
(ISO 3166-2, US-CA, DE-BY) besides the EU or a country. The app adds
"(EU)" to a member country and the country to a subdivision ("Germany
(EU)", "California, United States", "Bavaria, Germany (EU)"), in
English and German, and shows the most specific flag there is: a
subdivision's own where the flag package has one, else its country's.
Subdivision names come from Unicode CLDR 48.2 (tool/subdivision_names.py),
bundled with their licence, which the app registers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_app/test/app/instance_gate_test.dart

@@ -51,6 +51,7 @@ void main() {
     bool signedOut = false,
     Set<Instance> answering = const {},
     Map<Instance, InstanceLocations> locations = const {},
+    SubdivisionNames subdivisionNames = const MemorySubdivisionNames({}),
   }) async {
     tester.view.physicalSize = const Size(412, 900);
     tester.view.devicePixelRatio = 1;
@@ -68,7 +69,10 @@ void main() {
         checker: FakeInstanceChecker(answering, locations),
         countryNames: MemoryCountryNames(const {
           'CH': {'en': 'Switzerland'},
+          'DE': {'en': 'Germany'},
+          'US': {'en': 'United States'},
         }),
+        subdivisionNames: subdivisionNames,
         readLook: () async => (themeMode: ThemeMode.light, locale: null),
         open: (instance) async {
           opened.add(instance);
@@ -127,6 +131,30 @@ void main() {
     expect(find.byType(Flag), findsOne);
   });
 
+  testWidgets('an instance may say where more precisely: a state, a region', (
+    tester,
+  ) async {
+    await start(
+      tester,
+      answering: {builtIn},
+      locations: {
+        builtIn: const InstanceLocations(data: 'US-CA', backups: 'DE-BY'),
+      },
+      subdivisionNames: const MemorySubdivisionNames({
+        'DE-BY': {'en': 'Bavaria'},
+        'US-CA': {'en': 'California'},
+      }),
+    );
+
+    expect(
+      find.text(
+        'Data: California, United States\nBackups: Bavaria, Germany (EU)',
+      ),
+      findsOne,
+    );
+    expect(find.byType(Flag), findsOne);
+  });
+
   testWidgets('an instance saying nothing, or not answering, comes with the '
       'app, without a flag', (tester) async {
     await start(tester);