feat(bibliothèque): migration Drift v16, seed basket et seeding au démarrage (ticket #80)

Ajoute la migration Drift v16 (enum ExerciseCategory, champ isExample sur
exercises/programs/workout_templates, table local_seed_metadata), le
contenu seed basket déterministe (21 exercices, 1 programme, 1 séance-
modèle) dans lib/application/starter_content/, les ports
StarterSeedStateRepository/StarterContentRepository et le use case
SeedStarterContentUseCase branché dans AppBootstrap.create().

Validé GO par QA/Main : dart analyze propre, suite complète 167 tests
(4 échecs préexistants sans rapport avec ce lot), 4 nouveaux tests seed
tous verts.

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

lib/application/use_cases.dart

@@ -2,9 +2,76 @@ import 'dart:convert';
 
 import '../domain/domain.dart';
 import 'ports.dart';
+import 'starter_content/basket_starter_seed_v1.dart';
+import 'starter_content/starter_content.dart';
 
 const Object _useCaseUnchanged = Object();
 
+enum StarterSeedStatus { inserted, skippedAlreadyApplied, skippedNotEmpty }
+
+final class StarterSeedResult {
+  const StarterSeedResult({required this.status, required this.appliedVersion});
+
+  final StarterSeedStatus status;
+  final int appliedVersion;
+}
+
+final class SeedStarterContentUseCase {
+  const SeedStarterContentUseCase({
+    required this.seedStateRepository,
+    required this.contentRepository,
+    required this.clock,
+    required this.originDeviceId,
+  });
+
+  final StarterSeedStateRepository seedStateRepository;
+  final StarterContentRepository contentRepository;
+  final Clock clock;
+  final String originDeviceId;
+
+  Future<StarterSeedResult> run() async {
+    final appliedVersion = await seedStateRepository
+        .readAppliedStarterSeedVersion();
+    if (appliedVersion >= starterSeedVersion) {
+      return const StarterSeedResult(
+        status: StarterSeedStatus.skippedAlreadyApplied,
+        appliedVersion: starterSeedVersion,
+      );
+    }
+
+    final now = clock.now();
+    final isEmpty = await contentRepository.isLocalContentEmpty();
+    if (!isEmpty) {
+      await seedStateRepository.writeAppliedStarterSeedVersion(
+        starterSeedVersion,
+        now,
+      );
+      return const StarterSeedResult(
+        status: StarterSeedStatus.skippedNotEmpty,
+        appliedVersion: starterSeedVersion,
+      );
+    }
+
+    await contentRepository.insertStarterContent(
+      buildStarterContent(
+        exerciseSeeds: basketStarterExerciseSeedsV1,
+        programSeed: basketStarterProgramSeedV1,
+        templateSeed: basketStarterWorkoutTemplateSeedV1,
+        now: now,
+        originDeviceId: originDeviceId,
+      ),
+    );
+    await seedStateRepository.writeAppliedStarterSeedVersion(
+      starterSeedVersion,
+      now,
+    );
+    return const StarterSeedResult(
+      status: StarterSeedStatus.inserted,
+      appliedVersion: starterSeedVersion,
+    );
+  }
+}
+
 final class AuthUseCases {
   const AuthUseCases({
     required this.tokenStore,