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_base_client/lib/src/protocol/instance/instance_basics.dart

@@ -73,9 +73,9 @@ abstract class InstanceBasics
   int minimumAppBuild;
 
   /// Where this instance keeps people's data, as its operator says
-  /// (DATA_LOCATION): a country's code (ISO 3166-1 alpha-2, `CH`) or `EU`;
-  /// where the disks are, not which law governs. Null where the operator
-  /// says nothing.
+  /// (DATA_LOCATION): `EU`, a country's code (ISO 3166-1 alpha-2, `DE`) or a
+  /// subdivision's (ISO 3166-2, `US-CA`, `DE-BY`), in capitals; where the
+  /// disks are, not which law governs. Null where the operator says nothing.
   String? dataLocation;
 
   /// Where it keeps its backups (BACKUP_LOCATION): as [dataLocation], or