feat(application): couche application avec use cases et repositories

Ajoute les entités du domaine (domain/entities.dart), les ports de
repository (application/ports.dart), les use cases (application/use_cases.dart)
et leur implémentation Drift (infrastructure/local/drift_repositories.dart).
flutter analyze propre, tests unitaires verts, build APK debug validé.

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

test/application/use_cases_test.dart

@@ -0,0 +1,117 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gametime/application/application.dart';
+import 'package:gametime/domain/domain.dart';
+
+void main() {
+  test('Exercise requires at least one active measure', () {
+    expect(
+      () => Exercise(
+        metadata: _metadata('exercise-1'),
+        name: 'Push up',
+        hasTimeMeasure: false,
+        hasRepsMeasure: false,
+        hasScoreMeasure: false,
+      ),
+      throwsA(isA<DomainException>()),
+    );
+  });
+
+  test('Workout template use case rejects active measure overrides', () async {
+    final useCase = WorkoutTemplateUseCases(
+      templateRepository: _FakeWorkoutTemplateRepository(),
+      programRepository: _FakeProgramRepository(),
+      clock: _FakeClock(DateTime.utc(2026, 7, 17, 12)),
+      ids: _FakeIds(),
+      originDeviceId: 'device-1',
+    );
+
+    await expectLater(
+      useCase.overrideExerciseTargets(
+        workoutTemplateProgramId: 'template-program-1',
+        snapshotProgramExerciseId: 'exercise-snapshot-1',
+        attemptedMeasureOverride: {WorkoutMeasure.reps},
+      ),
+      throwsA(isA<DomainException>()),
+    );
+  });
+
+  test('Active session elapsed time is based on persisted timestamps', () {
+    final clock = _FakeClock(DateTime.utc(2026, 7, 17, 12));
+    final session = ActiveWorkoutSession(
+      metadata: _metadata('session-1'),
+      status: ActiveWorkoutStatus.running,
+      startedAt: clock.now(),
+      lastPersistedAt: clock.now(),
+      elapsedActiveMs: 0,
+      currentProgramIndex: 0,
+      currentExerciseIndex: 0,
+      currentSetIndex: 0,
+      resolvedTemplateSnapshotJson: '{}',
+    );
+
+    clock.value = clock.value.add(const Duration(seconds: 30));
+    final paused = session.pause(clock.now());
+    expect(paused.elapsedActiveMs, 30000);
+
+    clock.value = clock.value.add(const Duration(minutes: 5));
+    final resumed = paused.resume(clock.now());
+    expect(resumed.elapsedActiveMillisecondsAt(clock.now()), 30000);
+
+    clock.value = clock.value.add(const Duration(seconds: 15));
+    expect(resumed.elapsedActiveMillisecondsAt(clock.now()), 45000);
+  });
+}
+
+EntityMetadata _metadata(String id) {
+  return EntityMetadata(
+    id: id,
+    createdAt: DateTime.utc(2026, 7, 17),
+    updatedAt: DateTime.utc(2026, 7, 17),
+    originDeviceId: 'device-1',
+  );
+}
+
+final class _FakeClock implements Clock {
+  _FakeClock(this.value);
+
+  DateTime value;
+
+  @override
+  DateTime now() => value;
+}
+
+final class _FakeIds implements IdGenerator {
+  var _next = 0;
+
+  @override
+  String newId() {
+    _next += 1;
+    return 'id-$_next';
+  }
+}
+
+final class _FakeWorkoutTemplateRepository
+    implements WorkoutTemplateRepository {
+  @override
+  Future<WorkoutTemplate?> findById(String id) async => null;
+
+  @override
+  Future<void> save(WorkoutTemplate template) async {}
+
+  @override
+  Future<void> saveOverride(WorkoutTemplateExerciseOverride override) async {}
+
+  @override
+  Future<void> saveProgram(WorkoutTemplateProgram program) async {}
+}
+
+final class _FakeProgramRepository implements ProgramRepository {
+  @override
+  Future<Program?> findById(String id) async => null;
+
+  @override
+  Future<void> save(Program program) async {}
+
+  @override
+  Future<void> saveExercise(ProgramExercise exercise) async {}
+}