Stage 3: Plan editor with Steps, Supersets and reordering

- Plan model with immutable edits: add with Mode defaults, move, remove,
  Superset with next, take a member out, ungroup; Stretching length
  estimate from holds, sides, rounds and Transitions
- drift database (plans table, items as JSON, ADR 0005) and
  PlanRepository; Plans list per Mode with rename/duplicate/delete
- Editor: drag handles, step editor sheet (sets, reps or time, optional
  kg; hold, both sides, rounds; Superset sets and rest between),
  pause between holds for Stretching Plans
- Exercise picker reusing the Library browser; Add to plan from the
  Exercise detail page
- Theme: Mode-styled snackbar, FAB, menus, segmented buttons, switches

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

test/views/plan_editor_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:zenxercise/src/modes/mode.dart';
+import 'package:zenxercise/src/plans/models/plan.dart';
+import 'package:zenxercise/src/plans/plan_repository.dart';
+
+import '../support/test_app.dart';
+import '../support/test_database.dart';
+
+void main() {
+  late PlanRepository plans;
+
+  setUp(() {
+    final db = testDatabase();
+    addTearDown(db.close);
+    plans = PlanRepository(db);
+  });
+
+  /// A Workout Plan with two Squat Steps, open in the editor.
+  Future<Plan> openWorkoutPlan(WidgetTester tester) async {
+    final plan = await plans.create(Mode.workout, 'Legs');
+    await plans.save(plan.withExerciseAdded('Barbell_Squat').withExerciseAdded('Barbell_Squat'));
+    usePhoneScreen(tester);
+    await pumpApp(tester, plans: plans, prefs: {'mode': 'workout'});
+    await tester.tap(find.text('Legs'));
+    await tester.pumpAndSettle();
+    return plan;
+  }
+
+  testWidgets('a new Plan is named, filled from the picker and listed with its count', (tester) async {
+    usePhoneScreen(tester);
+    await pumpApp(tester, plans: plans);
+
+    await tester.tap(find.text('New plan'));
+    await tester.pumpAndSettle();
+    await tester.enterText(find.byType(TextField), 'Morning');
+    await tester.pump();
+    await tester.tap(find.text('Create'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Morning'), findsOneWidget);
+    expect(find.text('No exercises yet'), findsWidgets);
+
+    await tester.tap(find.text('Add exercises'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('90/90 Hamstring'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Calf Stretch'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Done'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('90/90 Hamstring'), findsOneWidget);
+    expect(find.text('Calf Stretch'), findsOneWidget);
+    // Two 30 s holds and one 5 s Transition.
+    expect(find.text('2 exercises · about 1 min'), findsOneWidget);
+
+    await tester.pageBack();
+    await tester.pumpAndSettle();
+
+    expect(find.text('Morning'), findsOneWidget);
+    expect(find.text('2 exercises · about 1 min'), findsOneWidget);
+  });
+
+  testWidgets('editing a Step saves at once and shows in its summary', (tester) async {
+    final plan = await openWorkoutPlan(tester);
+
+    await tester.tap(find.text('Barbell Squat').first);
+    await tester.pumpAndSettle();
+    await tester.tap(find.byTooltip('Sets +'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Add a target weight'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Done'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('4 × 10 reps · 20 kg'), findsOneWidget);
+    expect((await plans.get(plan.id))!.items.first, isA<WorkoutStep>().having((s) => s.sets, 'sets', 4));
+  });
+
+  testWidgets('two Steps become a Superset and split again', (tester) async {
+    await openWorkoutPlan(tester);
+
+    // The first Step's menu; the Plan's own menu in the app bar comes last.
+    await tester.tap(find.byTooltip('More actions').first);
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Superset with next'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Superset · 3 sets'), findsOneWidget);
+    expect(find.text('10 reps'), findsNWidgets(2));
+
+    await tester.tap(find.byTooltip('More actions').first);
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Ungroup'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Superset · 3 sets'), findsNothing);
+    expect(find.text('3 × 10 reps'), findsNWidgets(2));
+  });
+
+  testWidgets('deleting the Plan from its editor returns to the list', (tester) async {
+    await openWorkoutPlan(tester);
+
+    await tester.tap(find.byTooltip('More actions').last);
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Delete'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.widgetWithText(FilledButton, 'Delete'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Legs'), findsNothing);
+    expect(find.text('No plans yet'), findsOneWidget);
+  });
+
+  testWidgets('an Exercise is added to a Plan from its detail page', (tester) async {
+    final plan = await plans.create(Mode.stretching, 'Evening');
+    usePhoneScreen(tester);
+    await pumpApp(tester, plans: plans);
+    await tester.tap(find.byTooltip('Library'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Calf Stretch'));
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.text('Add to plan'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Evening'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Added to Evening'), findsOneWidget);
+    expect((await plans.get(plan.id))!.items.single, isA<StretchingStep>());
+  });
+}