feat(ui): écran Composition de séance-modèle

Ajoute l'écran de composition de séance-modèle
(presentation/workout_template_screen.dart), avec les ajustements
application/domaine/repositories nécessaires et la navigation depuis
l'accueil. flutter analyze propre, 12/12 tests verts, build APK debug
validé.

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

lib/application/use_cases.dart

@@ -398,6 +398,14 @@ final class WorkoutTemplateUseCases {
   final IdGenerator ids;
   final String originDeviceId;
 
+  Future<WorkoutTemplate?> findById(String id) {
+    return templateRepository.findById(id);
+  }
+
+  Future<List<WorkoutTemplate>> listActive() {
+    return templateRepository.listActive();
+  }
+
   Future<WorkoutTemplate> create({required String name}) async {
     final now = clock.now();
     final template = WorkoutTemplate(
@@ -408,6 +416,78 @@ final class WorkoutTemplateUseCases {
     return template;
   }
 
+  Future<WorkoutTemplate> saveConfigured({
+    String? id,
+    required String name,
+    required List<WorkoutTemplateProgramConfig> programs,
+    required List<WorkoutTemplateExerciseOverrideConfig> overrides,
+  }) async {
+    final now = clock.now();
+    final existing = id == null ? null : await templateRepository.findById(id);
+    if (id != null && existing == null) {
+      throw const DomainException('Workout template not found.');
+    }
+    final templateId = id ?? ids.newId();
+    final metadata =
+        existing?.metadata.touch(now) ??
+        EntityMetadata(
+          id: templateId,
+          createdAt: now,
+          updatedAt: now,
+          originDeviceId: originDeviceId,
+        );
+    final templatePrograms = <WorkoutTemplateProgram>[];
+    final programIdsByClientKey = <String, String>{};
+    for (var index = 0; index < programs.length; index++) {
+      final input = programs[index];
+      final programMetadata =
+          input.existingMetadata?.touch(now) ??
+          _newMetadata(ids, originDeviceId, now);
+      programIdsByClientKey[input.clientKey] = programMetadata.id;
+      templatePrograms.add(
+        WorkoutTemplateProgram(
+          metadata: programMetadata,
+          workoutTemplateId: templateId,
+          sourceProgramId: input.sourceProgramId,
+          position: index,
+          programNameSnapshot: input.programNameSnapshot,
+          defaultRestSecondsSnapshot: input.defaultRestSecondsSnapshot,
+          programSnapshotJson: input.programSnapshotJson,
+        ),
+      );
+    }
+    final templateOverrides = <WorkoutTemplateExerciseOverride>[];
+    for (final input in overrides) {
+      final workoutTemplateProgramId =
+          programIdsByClientKey[input.workoutTemplateProgramClientKey];
+      if (workoutTemplateProgramId == null) {
+        throw const DomainException('Workout template program not found.');
+      }
+      templateOverrides.add(
+        WorkoutTemplateExerciseOverride(
+          metadata:
+              input.existingMetadata?.touch(now) ??
+              _newMetadata(ids, originDeviceId, now),
+          workoutTemplateProgramId: workoutTemplateProgramId,
+          snapshotProgramExerciseId: input.snapshotProgramExerciseId,
+          setsCountOverride: input.setsCountOverride,
+          targetTimeSecondsOverride: input.targetTimeSecondsOverride,
+          targetRepsOverride: input.targetRepsOverride,
+          targetScoreOverride: input.targetScoreOverride,
+        ),
+      );
+    }
+    final template = WorkoutTemplate(
+      metadata: metadata,
+      name: name,
+      lastStartedAt: existing?.lastStartedAt,
+      programs: templatePrograms,
+      overrides: templateOverrides,
+    );
+    await templateRepository.replaceComposition(template, now);
+    return template;
+  }
+
   Future<WorkoutTemplateProgram> addProgramSnapshot({
     required String workoutTemplateId,
     required String programId,
@@ -457,6 +537,44 @@ final class WorkoutTemplateUseCases {
   }
 }
 
+final class WorkoutTemplateProgramConfig {
+  const WorkoutTemplateProgramConfig({
+    required this.clientKey,
+    this.existingMetadata,
+    this.sourceProgramId,
+    required this.programNameSnapshot,
+    required this.defaultRestSecondsSnapshot,
+    required this.programSnapshotJson,
+  });
+
+  final String clientKey;
+  final EntityMetadata? existingMetadata;
+  final String? sourceProgramId;
+  final String programNameSnapshot;
+  final int defaultRestSecondsSnapshot;
+  final String programSnapshotJson;
+}
+
+final class WorkoutTemplateExerciseOverrideConfig {
+  const WorkoutTemplateExerciseOverrideConfig({
+    this.existingMetadata,
+    required this.workoutTemplateProgramClientKey,
+    required this.snapshotProgramExerciseId,
+    this.setsCountOverride,
+    this.targetTimeSecondsOverride,
+    this.targetRepsOverride,
+    this.targetScoreOverride,
+  });
+
+  final EntityMetadata? existingMetadata;
+  final String workoutTemplateProgramClientKey;
+  final String snapshotProgramExerciseId;
+  final int? setsCountOverride;
+  final int? targetTimeSecondsOverride;
+  final int? targetRepsOverride;
+  final double? targetScoreOverride;
+}
+
 final class ActiveWorkoutSessionUseCases {
   const ActiveWorkoutSessionUseCases({
     required this.sessionRepository,