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/unit/map/map_source_test.dart

@@ -0,0 +1,68 @@
+import 'package:halkyon_train_server/src/map/map_source_config.dart';
+import 'package:test/test.dart';
+
+/// The instance's map source as its operator sets it (ADR 0030, D11, D22).
+void main() {
+  test('without a setting it is OpenFreeMap, named, with its attribution', () {
+    final source = mapSourceFrom(const {});
+
+    expect(source.name, 'OpenFreeMap');
+    expect(source.styleUrl, 'https://tiles.openfreemap.org/styles/liberty');
+    expect(source.attribution, contains('OpenStreetMap'));
+    expect(source.aboutUrl, 'https://openfreemap.org');
+  });
+
+  test("an operator's provider is named as they set it", () {
+    final source = mapSourceFrom(const {
+      'MAP_STYLE_URL':
+          'https://api.maptiler.com/maps/outdoor-v2/style.json?key=k',
+      'MAP_SOURCE_NAME': 'MapTiler',
+      'MAP_ATTRIBUTION': '© MapTiler © OpenStreetMap contributors',
+      'MAP_ABOUT_URL': 'https://www.maptiler.com/privacy-policy/',
+    });
+
+    expect(source.name, 'MapTiler');
+    expect(
+      source.styleUrl,
+      'https://api.maptiler.com/maps/outdoor-v2/style.json?key=k',
+    );
+    expect(source.attribution, '© MapTiler © OpenStreetMap contributors');
+    expect(source.aboutUrl, 'https://www.maptiler.com/privacy-policy/');
+  });
+
+  test('a provider without a name is named by its host, and credits '
+      'OpenStreetMap', () {
+    final source = mapSourceFrom(const {
+      'MAP_STYLE_URL': 'https://maps.example.org/style.json',
+    });
+
+    expect(source.name, 'maps.example.org');
+    expect(source.attribution, '© OpenStreetMap contributors');
+    expect(source.aboutUrl, isNull);
+  });
+
+  test("a style that isn't HTTPS, or isn't an address, is never used: the "
+      'map stays OpenFreeMap', () {
+    for (final url in [
+      'http://maps.example.org/style.json',
+      'maps.example.org/style.json',
+      'https://',
+      '  ',
+    ]) {
+      expect(
+        mapSourceFrom({'MAP_STYLE_URL': url}).name,
+        'OpenFreeMap',
+        reason: url,
+      );
+    }
+  });
+
+  test("an about page that isn't HTTPS is left out", () {
+    final source = mapSourceFrom(const {
+      'MAP_STYLE_URL': 'https://maps.example.org/style.json',
+      'MAP_ABOUT_URL': 'javascript:alert(1)',
+    });
+
+    expect(source.aboutUrl, isNull);
+  });
+}