Stage 1: project setup, Exercise Library, both Mode designs and the Mode switch

- Flutter Android app on CookIT's stack (provider, shared_preferences, gen-l10n)
- tools/exercise-import turns free-exercise-db into 876 bundled Exercises
  with 1,746 WebP images (20 MB); stretching -> Stretching, rest -> Workout
- ZenStyle tokens per Mode: calm rounded sage/teal with breath ripples vs.
  dark ember-to-red with floor-tape slashes; the theme morphs at each
  Mode's own pace
- Remembered global Mode switch, Plans / Library / History tabs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/support/test_app.dart

@@ -0,0 +1,49 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:provider/provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:zenxercise/src/app.dart';
+import 'package:zenxercise/src/exercises/exercise.dart';
+import 'package:zenxercise/src/exercises/exercise_library.dart';
+import 'package:zenxercise/src/modes/mode.dart';
+import 'package:zenxercise/src/settings/settings_controller.dart';
+
+Exercise exercise(String id, Mode mode, {String? name, int imageCount = 0}) => Exercise(
+  id: id,
+  name: name ?? id.replaceAll('_', ' '),
+  mode: mode,
+  category: mode == Mode.stretching ? 'stretching' : 'strength',
+  level: 'beginner',
+  equipment: 'body only',
+  primaryMuscles: const ['hamstrings'],
+  secondaryMuscles: const [],
+  instructions: const ['Breathe.'],
+  imageCount: imageCount,
+);
+
+final sampleLibrary = ExerciseLibrary([
+  exercise('Hamstring_Stretch', Mode.stretching),
+  exercise('Calf_Stretch', Mode.stretching),
+  exercise('Barbell_Squat', Mode.workout),
+]);
+
+/// The whole app over [library], with preferences starting from [prefs].
+Future<SettingsController> pumpApp(
+  WidgetTester tester, {
+  ExerciseLibrary? library,
+  Map<String, Object> prefs = const {},
+}) async {
+  SharedPreferences.setMockInitialValues(prefs);
+  final settings = SettingsController(SettingsService());
+  await settings.loadSettings();
+  await tester.pumpWidget(
+    MultiProvider(
+      providers: [
+        ChangeNotifierProvider.value(value: settings),
+        Provider.value(value: library ?? sampleLibrary),
+      ],
+      child: const ZenXerciseApp(),
+    ),
+  );
+  await tester.pumpAndSettle();
+  return settings;
+}