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>

README.md

@@ -24,6 +24,9 @@ tests in its folder (`dart test`, or `flutter test` for `halkyon_ui`, its
 example and `halkyon_app`). `halkyon_base_server`'s tests start Serverpod's embedded PostgreSQL by
 themselves and need a git-ignored `config/passwords.yaml` (see its README).
 
+`tool/subdivision_names.py` writes `halkyon_app`'s names of subdivisions from a
+release of Unicode CLDR (`python3 -I tool/subdivision_names.py release-48-2`).
+
 Licences: the server package `halkyon_base_server` is under the Server Side
 Public License 1.0, as the Halkyon servers are; every other package under the
 GNU Affero General Public License 3.0 or later.