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/lib/src/instance/cldr_license.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+import 'package:halkyon_app/src/instance/flag_icons_license.dart';
+
+/// Adds Unicode CLDR's notice to the app's licence list, beside the
+/// packages' own: the subdivisions' names come from it
+/// (`AssetSubdivisionNames`), and its licence asks that its notice go with
+/// them.
+void registerCldrLicense() => LicenseRegistry.addLicense(() async* {
+  yield LicenseEntryWithLineBreaks(
+    const ['Unicode CLDR'],
+    await rootBundle.loadString(cldrLicenseAsset),
+  );
+});
+
+/// Where the notice is, among this package's assets: verbatim from the
+/// release the names come from.
+const cldrLicenseAsset =
+    'packages/halkyon_app/assets/subdivisions/LICENSE-CLDR.txt';
+
+/// Adds every notice the package's own assets ask for to the app's licence
+/// list: the flags' ([registerFlagIconsLicense]) and Unicode CLDR's
+/// ([registerCldrLicense]). An app calls it once at startup.
+void registerHalkyonAppLicenses() {
+  registerFlagIconsLicense();
+  registerCldrLicense();
+}