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/domain/entities.dart

@@ -10,6 +10,17 @@ enum ScoreInputMode { manual, stopwatch }
 
 enum ExerciseStepType { time, reps }
 
+enum ExerciseCategory {
+  shoot,
+  freeThrows,
+  dribble,
+  finishing,
+  conditioning,
+  defense,
+  mobility,
+  uncategorized,
+}
+
 enum ActiveWorkoutStatus { running, paused, savedExit, completed, abandoned }
 
 enum SetResultStatus { completed, skipped }
@@ -321,6 +332,8 @@ final class Exercise {
     this.defaultTargetScore,
     this.defaultTargetScoreTimeMs,
     this.autoStartNextTimedStep = true,
+    this.category = ExerciseCategory.uncategorized,
+    this.isExample = false,
     List<ExerciseStep> steps = const [],
     this.archivedAt,
   }) : name = _nonBlank(name, 'Exercise name'),
@@ -379,6 +392,8 @@ final class Exercise {
   final double? defaultTargetScore;
   final int? defaultTargetScoreTimeMs;
   final bool autoStartNextTimedStep;
+  final ExerciseCategory category;
+  final bool isExample;
   final List<ExerciseStep> steps;
   final DateTime? archivedAt;
 
@@ -414,6 +429,8 @@ final class Exercise {
     Object? defaultTargetScore = _unchanged,
     Object? defaultTargetScoreTimeMs = _unchanged,
     bool? autoStartNextTimedStep,
+    ExerciseCategory? category,
+    bool? isExample,
     Object? steps = _unchanged,
     Object? archivedAt = _unchanged,
   }) {
@@ -463,6 +480,8 @@ final class Exercise {
           : defaultTargetScoreTimeMs as int?,
       autoStartNextTimedStep:
           autoStartNextTimedStep ?? this.autoStartNextTimedStep,
+      category: category ?? this.category,
+      isExample: isExample ?? this.isExample,
       steps: steps == _unchanged ? this.steps : steps as List<ExerciseStep>,
       archivedAt: archivedAt == _unchanged
           ? this.archivedAt
@@ -532,6 +551,7 @@ final class Program {
     required this.metadata,
     required String name,
     required this.defaultRestSeconds,
+    this.isExample = false,
     this.exercises = const [],
   }) : name = _nonBlank(name, 'Program name') {
     _requireNonNegative(defaultRestSeconds, 'Default rest seconds');
@@ -540,6 +560,7 @@ final class Program {
   final EntityMetadata metadata;
   final String name;
   final int defaultRestSeconds;
+  final bool isExample;
   final List<ProgramExercise> exercises;
 
   Program copyWith({
@@ -547,11 +568,13 @@ final class Program {
     EntityMetadata? metadata,
     String? name,
     int? defaultRestSeconds,
+    bool? isExample,
   }) {
     return Program(
       metadata: metadata ?? this.metadata,
       name: name ?? this.name,
       defaultRestSeconds: defaultRestSeconds ?? this.defaultRestSeconds,
+      isExample: isExample ?? this.isExample,
       exercises: exercises ?? this.exercises,
     );
   }
@@ -745,6 +768,7 @@ final class WorkoutTemplate {
     required this.metadata,
     required String name,
     this.lastStartedAt,
+    this.isExample = false,
     this.programs = const [],
     this.overrides = const [],
   }) : name = _nonBlank(name, 'Workout template name');
@@ -752,6 +776,7 @@ final class WorkoutTemplate {
   final EntityMetadata metadata;
   final String name;
   final DateTime? lastStartedAt;
+  final bool isExample;
   final List<WorkoutTemplateProgram> programs;
   final List<WorkoutTemplateExerciseOverride> overrides;
 }