feat(watch): clôture lot #91 - fréquence cardiaque live, notifications de séance et finitions montre

Consolide le lot applicatif watch companion validé :
- télémétrie fréquence cardiaque live remontée montre -> téléphone
  (collecteur watch, adapter Wear Data Layer, persistance Drift,
  propagation aux écrans historique/programme/profil/exécution)
- notifications de séance en arrière-plan côté téléphone (service
  foreground de statut + passerelle applicative)
- finitions montre : chrono d'étape, score d'étape, retrait du bouton
  "lancer une séance", thème, icônes et polices watch_app

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/test/sync_api_test.dart

@@ -62,6 +62,140 @@ void main() {
     ]);
     expect(repository.items.single.clientId, 'exercise-1');
   });
+
+  test('pull returns synced items and filters them with since query', () async {
+    final repository = _FakeSyncedResourceRepository()
+      ..items.addAll([
+        SyncedResource(
+          serverId: 'resource-1',
+          ownerUserId: 'user-1',
+          resourceType: SyncedResourceType.exercise,
+          clientId: 'exercise-1',
+          payloadJson: {'name': 'Squat'},
+          schemaVersion: 1,
+          clientUpdatedAt: DateTime.utc(2026, 7, 19, 10),
+          serverUpdatedAt: DateTime.utc(2026, 7, 19, 11),
+        ),
+        SyncedResource(
+          serverId: 'resource-2',
+          ownerUserId: 'user-1',
+          resourceType: SyncedResourceType.program,
+          clientId: 'program-1',
+          payloadJson: {'name': 'Programme A'},
+          schemaVersion: 2,
+          clientUpdatedAt: DateTime.utc(2026, 7, 19, 11),
+          serverUpdatedAt: DateTime.utc(2026, 7, 19, 12, 30),
+        ),
+      ]);
+    final handler = buildApiHandler(syncApi: _syncApi(resources: repository));
+
+    final response = await handler(
+      Request(
+        'GET',
+        Uri.parse(
+          'http://localhost/sync/pull?since=2026-07-19T12:00:00Z',
+        ),
+        headers: {'authorization': 'Bearer valid-token'},
+      ),
+    );
+
+    final body = jsonDecode(await response.readAsString()) as Map;
+    final items = body['items'] as List;
+
+    expect(response.statusCode, 200);
+    expect(body['serverCursor'], '2026-07-19T12:30:00.000Z');
+    expect(items, hasLength(1));
+    expect((items.single as Map)['clientId'], 'program-1');
+    expect((items.single as Map)['resourceType'], 'program');
+  });
+
+  test('pull returns 400 for invalid since query parameter', () async {
+    final handler = buildApiHandler(syncApi: _syncApi());
+
+    final response = await handler(
+      Request(
+        'GET',
+        Uri.parse('http://localhost/sync/pull?since=not-a-date'),
+        headers: {'authorization': 'Bearer valid-token'},
+      ),
+    );
+
+    expect(response.statusCode, 400);
+    expect(
+      jsonDecode(await response.readAsString()),
+      {'error': 'Invalid date format'},
+    );
+  });
+
+  test('exchange returns push results followed by pulled items', () async {
+    final repository = _FakeSyncedResourceRepository()
+      ..items.add(
+        SyncedResource(
+          serverId: 'existing-1',
+          ownerUserId: 'user-1',
+          resourceType: SyncedResourceType.workoutHistory,
+          clientId: 'history-1',
+          payloadJson: {'score': 12},
+          schemaVersion: 1,
+          clientUpdatedAt: DateTime.utc(2026, 7, 19, 8),
+          serverUpdatedAt: DateTime.utc(2026, 7, 19, 9),
+        ),
+      );
+    final handler = buildApiHandler(syncApi: _syncApi(resources: repository));
+
+    final response = await handler(
+      Request(
+        'POST',
+        Uri.parse('http://localhost/sync/exchange'),
+        headers: {'authorization': 'Bearer valid-token'},
+        body: jsonEncode({
+          'deviceId': 'device-1',
+          'since': '2026-07-19T08:30:00Z',
+          'items': [
+            {
+              'resourceType': 'exercise',
+              'clientId': 'exercise-2',
+              'schemaVersion': 1,
+              'clientUpdatedAt': '2026-07-19T10:00:00Z',
+              'payload': {'name': 'Lunge'},
+            },
+          ],
+        }),
+      ),
+    );
+
+    final body = jsonDecode(await response.readAsString()) as Map;
+    final pushResults = body['pushResults'] as List;
+    final items = body['items'] as List;
+
+    expect(response.statusCode, 200);
+    expect(pushResults, hasLength(1));
+    expect((pushResults.single as Map)['status'], 'accepted');
+    expect(items, hasLength(2));
+    expect(
+      items.map((item) => (item as Map)['clientId']),
+      containsAll(['history-1', 'exercise-2']),
+    );
+  });
+
+  test('exchange returns 400 when items is not a json array', () async {
+    final handler = buildApiHandler(syncApi: _syncApi());
+
+    final response = await handler(
+      Request(
+        'POST',
+        Uri.parse('http://localhost/sync/exchange'),
+        headers: {'authorization': 'Bearer valid-token'},
+        body: jsonEncode({'deviceId': 'device-1', 'items': 'not-a-list'}),
+      ),
+    );
+
+    expect(response.statusCode, 400);
+    expect(
+      jsonDecode(await response.readAsString()),
+      {'error': 'items must be a JSON array.'},
+    );
+  });
 }
 
 SyncApi _syncApi({_FakeSyncedResourceRepository? resources}) {