feat(train): the instance names its map source (ADR 0030, D11, D22)

Train's first endpoint of its own, map.source, names the map workouts
are drawn on, for people signed in only, as a provider's key may be in
its style's address: OpenFreeMap's Liberty style where the operator sets
nothing, else MAP_STYLE_URL (HTTPS only) with MAP_SOURCE_NAME,
MAP_ATTRIBUTION and MAP_ABOUT_URL. A model without a table: no
migration. D22 is recorded in ADR 0030.

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

apps/train/halkyon_train_server/test/integration/map/map_endpoint_test.dart

@@ -0,0 +1,36 @@
+import 'package:serverpod/serverpod.dart';
+import 'package:test/test.dart';
+
+import '../test_tools/serverpod_test_tools.dart';
+
+/// The map the app draws workouts on, as the instance names it (ADR 0030,
+/// D11, D22): for the people signed in, as the provider's key may be in it.
+void main() {
+  withServerpod('The map source', (sessionBuilder, endpoints) {
+    test('names OpenFreeMap to someone signed in, where the operator sets '
+        'nothing', () async {
+      final source = await endpoints.map.source(
+        sessionBuilder.copyWith(
+          authentication: AuthenticationOverride.authenticationInfo(
+            const Uuid().v7(),
+            {},
+          ),
+        ),
+      );
+
+      expect(source.name, 'OpenFreeMap');
+      expect(source.styleUrl, startsWith('https://tiles.openfreemap.org/'));
+    });
+
+    test('names nothing to nobody signed in', () async {
+      await expectLater(
+        endpoints.map.source(
+          sessionBuilder.copyWith(
+            authentication: AuthenticationOverride.unauthenticated(),
+          ),
+        ),
+        throwsA(isA<ServerpodUnauthenticatedException>()),
+      );
+    });
+  });
+}