merge(develop): clôture lot #91 Wear OS - fréquence cardiaque, notifications, finitions montre

Intègre le commit de clôture du lot #91 resté non fusionné. Conflits
attendus sur entities.dart, workout_execution_screen.dart et
watch_companion_projection_test.dart : arbitrage Architect - garder la
base feature/ticket91-wear-os-watch-sync sur ces 3 fichiers puis réinjecter
uniquement les invariants chronos utiles (Durée / Temps réalisé).

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

# Conflicts:
#	lib/domain/entities.dart
#	lib/presentation/workout_execution_screen.dart
#	test/application/watch_companion_projection_test.dart

lib/presentation/program_screen.dart

@@ -420,6 +420,7 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
 
   @override
   Widget build(BuildContext context) {
+    final canSave = !_saving && _exercises.isNotEmpty;
     return Scaffold(
       appBar: AppBar(
         title: Text(
@@ -436,15 +437,21 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
       ),
       bottomNavigationBar: SafeArea(
         minimum: const EdgeInsets.all(16),
-        child: FilledButton.icon(
-          onPressed: _saving ? null : _save,
-          icon: _saving
-              ? const SizedBox.square(
-                  dimension: 18,
-                  child: CircularProgressIndicator(strokeWidth: 2),
-                )
-              : const Icon(Icons.check),
-          label: const Text('Enregistrer'),
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            FilledButton.icon(
+              onPressed: canSave ? _save : null,
+              icon: _saving
+                  ? const SizedBox.square(
+                      dimension: 18,
+                      child: CircularProgressIndicator(strokeWidth: 2),
+                    )
+                  : const Icon(Icons.check),
+              label: const Text('Enregistrer'),
+            ),
+          ],
         ),
       ),
       body: Column(
@@ -495,7 +502,8 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
             child: _exercises.isEmpty
                 ? const _CenteredMessage(
                     title: 'Aucun exercice ajouté',
-                    message: 'Ajoute un exercice depuis la bibliothèque.',
+                    message:
+                        'Ajoute au moins un exercice pour enregistrer ce programme.',
                   )
                 : ReorderableListView.builder(
                     buildDefaultDragHandles: false,
@@ -595,6 +603,9 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
   }
 
   Future<void> _save() async {
+    if (_exercises.isEmpty) {
+      return;
+    }
     if (!_formKey.currentState!.validate()) {
       return;
     }
@@ -1402,7 +1413,7 @@ final class _CenteredMessage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Center(
-      child: Padding(
+      child: SingleChildScrollView(
         padding: const EdgeInsets.all(24),
         child: Column(
           mainAxisSize: MainAxisSize.min,