feat(online): partage sortant et boîte de réception (ticket #69)

Ajoute l'écran de partage sortant (presentation/share_screen.dart) et
la boîte de réception des partages (presentation/share_inbox_screen.dart),
avec les points d'entrée sur profile_screen.dart, home_screen.dart,
program_screen.dart et workout_template_screen.dart. flutter analyze
propre (mêmes infos préexistantes), 132/132 tests verts, build APK
debug validé. Dernier ticket de développement du chantier "Ajouter
les features serveur au client" (#63) — il ne reste que la QA finale
(#70).

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

lib/presentation/workout_template_screen.dart

@@ -4,6 +4,7 @@ import 'package:flutter/material.dart';
 
 import '../application/application.dart';
 import '../domain/domain.dart';
+import 'share_screen.dart';
 import 'workout_execution_screen.dart';
 
 final class WorkoutTemplateListScreen extends StatefulWidget {
@@ -15,6 +16,9 @@ final class WorkoutTemplateListScreen extends StatefulWidget {
     required this.historyUseCases,
     this.mediaUseCases,
     this.stepUseCases,
+    this.shareUseCases,
+    this.authUseCases,
+    this.syncUseCases,
     super.key,
   });
 
@@ -25,6 +29,9 @@ final class WorkoutTemplateListScreen extends StatefulWidget {
   final CloseWorkoutSessionUseCase closeUseCase;
   final WorkoutHistoryUseCases historyUseCases;
   final MediaUseCases? mediaUseCases;
+  final ShareUseCases? shareUseCases;
+  final AuthUseCases? authUseCases;
+  final SyncUseCases? syncUseCases;
 
   @override
   State<WorkoutTemplateListScreen> createState() =>
@@ -109,6 +116,9 @@ final class _WorkoutTemplateListScreenState
         builder: (context) => WorkoutTemplateFormScreen(
           workoutTemplateUseCases: widget.workoutTemplateUseCases,
           programUseCases: widget.programUseCases,
+          shareUseCases: widget.shareUseCases,
+          authUseCases: widget.authUseCases,
+          syncUseCases: widget.syncUseCases,
           template: template,
         ),
       ),
@@ -193,12 +203,18 @@ final class WorkoutTemplateFormScreen extends StatefulWidget {
   const WorkoutTemplateFormScreen({
     required this.workoutTemplateUseCases,
     required this.programUseCases,
+    this.shareUseCases,
+    this.authUseCases,
+    this.syncUseCases,
     this.template,
     super.key,
   });
 
   final WorkoutTemplateUseCases workoutTemplateUseCases;
   final ProgramUseCases programUseCases;
+  final ShareUseCases? shareUseCases;
+  final AuthUseCases? authUseCases;
+  final SyncUseCases? syncUseCases;
   final WorkoutTemplate? template;
 
   @override
@@ -241,6 +257,14 @@ final class _WorkoutTemplateFormScreenState
     return Scaffold(
       appBar: AppBar(
         title: Text(_isEditing ? 'Modifier la séance' : 'Créer une séance'),
+        actions: [
+          if (_isEditing && widget.shareUseCases != null)
+            IconButton(
+              tooltip: 'Partager',
+              icon: const Icon(Icons.ios_share),
+              onPressed: _shareTemplate,
+            ),
+        ],
       ),
       bottomNavigationBar: SafeArea(
         minimum: const EdgeInsets.all(16),
@@ -390,6 +414,25 @@ final class _WorkoutTemplateFormScreenState
     }
   }
 
+  Future<void> _shareTemplate() async {
+    final template = widget.template;
+    final shareUseCases = widget.shareUseCases;
+    if (template == null || shareUseCases == null) return;
+    await Navigator.of(context).push<void>(
+      MaterialPageRoute(
+        builder: (context) => ShareFormScreen(
+          shareUseCases: shareUseCases,
+          authUseCases: widget.authUseCases,
+          syncUseCases: widget.syncUseCases,
+          resourceType: ShareResourceType.workoutTemplate,
+          localResourceId: template.metadata.id,
+          resourceName: template.name,
+          resourceSummary: _templateSummary(template),
+        ),
+      ),
+    );
+  }
+
   void _showSnackBar(String message) {
     if (!mounted) return;
     ScaffoldMessenger.of(