fix(ui): popup de confirmation d'ajout d'exercice (ticket #24)

Corrige le popup de confirmation quand un exercice est ajouté sur
program_screen.dart. flutter analyze propre, 43/43 tests verts, build
APK debug validé. Ticket laissé en QA : validation manuelle sur APK
par l'utilisateur avant clôture.

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

lib/presentation/program_screen.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
 import '../application/application.dart';
@@ -121,6 +123,7 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
   late final TextEditingController _nameController;
   late final TextEditingController _defaultRestController;
   late final List<_ProgramExerciseDraft> _exercises;
+  Timer? _addedSnackBarTimer;
   var _saving = false;
 
   bool get _isEditing => widget.program != null;
@@ -145,6 +148,7 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
 
   @override
   void dispose() {
+    _addedSnackBarTimer?.cancel();
     _nameController.dispose();
     _defaultRestController.dispose();
     super.dispose();
@@ -253,12 +257,25 @@ final class _ProgramFormScreenState extends State<ProgramFormScreen> {
     setState(() {
       _exercises.add(draft);
     });
-    ScaffoldMessenger.of(context).showSnackBar(
+    final messenger = ScaffoldMessenger.of(context);
+    _addedSnackBarTimer?.cancel();
+    _addedSnackBarTimer = Timer(const Duration(seconds: 3), () {
+      if (mounted) {
+        messenger.hideCurrentSnackBar();
+      }
+    });
+    messenger.showSnackBar(
       SnackBar(
+        duration: const Duration(seconds: 3),
         content: const Text('Exercice ajouté'),
         action: SnackBarAction(
           label: 'Personnaliser',
-          onPressed: () => _customizeExercise(draft.key),
+          onPressed: () {
+            _addedSnackBarTimer?.cancel();
+            _addedSnackBarTimer = null;
+            messenger.hideCurrentSnackBar();
+            _customizeExercise(draft.key);
+          },
         ),
       ),
     );

test/presentation/program_screen_test.dart

@@ -103,6 +103,61 @@ void main() {
     },
   );
 
+  testWidgets(
+    'la popup exercice ajouté disparaît et se ferme à la personnalisation',
+    (tester) async {
+      final exerciseRepository = _FakeExerciseRepository()
+        ..exercises.add(
+          Exercise(
+            metadata: _metadata('exercise-1'),
+            name: 'Squat',
+            hasTimeMeasure: true,
+            hasRepsMeasure: false,
+            hasScoreMeasure: false,
+          ),
+        );
+
+      await tester.pumpWidget(
+        MaterialApp(
+          home: ProgramFormScreen(
+            programUseCases: _programUseCases(
+              _FakeProgramRepository(),
+              exerciseRepository,
+            ),
+            exerciseUseCases: _exerciseUseCases(exerciseRepository),
+          ),
+        ),
+      );
+
+      await tester.tap(find.text('Ajouter un exercice'));
+      await tester.pumpAndSettle();
+      await tester.tap(find.text('Squat'));
+      await tester.pumpAndSettle();
+
+      expect(find.text('Exercice ajouté'), findsOneWidget);
+
+      for (var i = 0; i < 5; i++) {
+        await tester.pump(const Duration(seconds: 1));
+      }
+      await tester.pump(const Duration(milliseconds: 500));
+
+      expect(find.text('Exercice ajouté'), findsNothing);
+
+      await tester.tap(find.text('Ajouter un exercice'));
+      await tester.pumpAndSettle();
+      await tester.tap(find.text('Squat').first);
+      await tester.pumpAndSettle();
+
+      expect(find.text('Exercice ajouté'), findsOneWidget);
+
+      await tester.tap(find.text('Personnaliser'));
+      await tester.pumpAndSettle();
+
+      expect(find.text('Exercice ajouté'), findsNothing);
+      expect(find.text("Personnaliser l'exercice"), findsOneWidget);
+    },
+  );
+
   testWidgets('affiche l’objectif de chrono pour un score en mode chrono', (
     tester,
   ) async {