feat(todo): a pin in the map's middle, and what is around it (ADR 0033, D32)

The location picker fills the screen with its map, the search floating
over it. A pin stays in the middle, lifting while the map moves, as
Molly's; where it lands the instance names the address and lists the
places around, as Threema's. That is `nearby` on the search endpoint,
for those signed in, the point neither kept nor logged, counted among
the searches: two lookups, as a plain one finds house numbers alone.

Fixes the map's credit, which overflowed a phone and was pale on white.

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/todo/halkyon_todo_server/test/integration/search/search_endpoint_test.dart

@@ -40,6 +40,33 @@ class _FakePhoton implements PlaceFinder {
     }
     return photonAnswer(answer);
   }
+
+  /// What was asked around a point: with tags for places to go, else for the
+  /// address.
+  final around_ = <({Set<String> tags, String? language})>[];
+
+  /// What Photon finds around a point.
+  List<Map<String, Object?>> address = const [
+    {'lat': 47.5, 'lon': 9.7, 'street': 'Danziger Weg', 'housenumber': '4'},
+  ];
+  List<Map<String, Object?>> neighbours = const [
+    {'lat': 47.5, 'lon': 9.7, 'name': 'EDEKA', 'osm_value': 'supermarket'},
+  ];
+
+  @override
+  Future<Map<String, Object?>> around(
+    PlacePoint at, {
+    required double radiusKm,
+    Set<String> tags = const {},
+    String? language,
+    required int limit,
+  }) async {
+    around_.add((tags: tags, language: language));
+    if (failing) {
+      throw const PhotonFailed('down');
+    }
+    return photonAnswer(tags.isEmpty ? address : neighbours);
+  }
 }
 
 Matcher _refused(String reason) =>
@@ -179,6 +206,93 @@ void main() {
       expect(places.first.name, 'EDEKA 0');
     });
 
+    test('around a point: the address, and the places to go to', () async {
+      final nearby = await endpoints.search.nearby(
+        alice,
+        PlacePoint(lat: 47.5, lon: 9.7),
+        language: 'de',
+      );
+
+      expect(nearby.spot?.name, 'Danziger Weg 4');
+      expect(nearby.places.single.name, 'EDEKA');
+      expect(photon.around_.map((asked) => asked.language), ['de', 'de']);
+      expect(photon.around_.map((asked) => asked.tags.isEmpty), [true, false]);
+    });
+
+    test('around a point nothing is found, without failing', () async {
+      photon
+        ..address = const []
+        ..neighbours = const [];
+      final nearby = await endpoints.search.nearby(
+        alice,
+        PlacePoint(lat: 47.5, lon: 9.7),
+      );
+      expect(nearby.spot, isNull);
+      expect(nearby.places, isEmpty);
+    });
+
+    test('the places around a point are no more than a search lists', () async {
+      photon.neighbours = [
+        for (var i = 0; i < PlaceSearch.limit + 2; i++)
+          {'lat': 1, 'lon': 2, 'name': 'Shop $i', 'osm_value': 'bakery'},
+      ];
+      final nearby = await endpoints.search.nearby(
+        alice,
+        PlacePoint(lat: 47.5, lon: 9.7),
+      );
+      expect(nearby.places, hasLength(PlaceSearch.limit));
+    });
+
+    test('tells nobody signed in what is around a point', () async {
+      await expectLater(
+        endpoints.search.nearby(
+          sessionBuilder.copyWith(
+            authentication: AuthenticationOverride.unauthenticated(),
+          ),
+          PlacePoint(lat: 47.5, lon: 9.7),
+        ),
+        throwsA(isA<ServerpodUnauthenticatedException>()),
+      );
+      expect(photon.around_, isEmpty);
+    });
+
+    test(
+      'refuses around a point off the earth, without asking Photon',
+      () async {
+        await expectLater(
+          endpoints.search.nearby(alice, PlacePoint(lat: 91, lon: 9.7)),
+          _refused('invalid'),
+        );
+        expect(photon.around_, isEmpty);
+      },
+    );
+
+    test('tells nothing around a point without a Photon', () async {
+      useSearch(PlaceSearch());
+      await expectLater(
+        endpoints.search.nearby(alice, PlacePoint(lat: 47.5, lon: 9.7)),
+        _refused('off'),
+      );
+    });
+
+    test("says Photon didn't answer around a point", () async {
+      photon.failing = true;
+      await expectLater(
+        endpoints.search.nearby(alice, PlacePoint(lat: 47.5, lon: 9.7)),
+        _refused('unreachable'),
+      );
+    });
+
+    test('a look around a point counts among the searches', () async {
+      for (var i = 0; i < PlaceSearch.perMinute; i++) {
+        await endpoints.search.nearby(alice, PlacePoint(lat: 47.5, lon: 9.7));
+      }
+      await expectLater(
+        endpoints.search.places(alice, 'Berlin'),
+        _refused('tooOften'),
+      );
+    });
+
     test("says Photon didn't answer where it fails", () async {
       photon.failing = true;
       await expectLater(