Add playable core UI: board painter, drag-and-drop, HUD, result overlay

CustomPainter board with gems/ghost/clear-flash, finger-lifted drag
with snap preview, combo text effect, HUD chips, phase overlays with
rescue stubs, demo stage. E2E widget test drives a real drag gesture.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/ui/board_geometry_test.dart

@@ -0,0 +1,46 @@
+import 'package:block_seasons/game/models/piece_library.dart';
+import 'package:block_seasons/ui/widgets/board_geometry.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  const geo = BoardGeometry(boardSize: 320); // cell = 40
+
+  group('cellAt', () {
+    test('maps points inside cells', () {
+      expect(geo.cellAt(const Offset(5, 5)), (0, 0));
+      expect(geo.cellAt(const Offset(60, 100)), (1, 2));
+      expect(geo.cellAt(const Offset(319, 319)), (7, 7));
+    });
+
+    test('returns null outside the board', () {
+      expect(geo.cellAt(const Offset(-1, 10)), isNull);
+      expect(geo.cellAt(const Offset(10, 321)), isNull);
+    });
+  });
+
+  group('cellRect', () {
+    test('returns the drawn rect for a cell', () {
+      final rect = geo.cellRect(2, 3);
+      expect(rect.left, 80);
+      expect(rect.top, 120);
+      expect(rect.width, 40);
+      expect(rect.height, 40);
+    });
+  });
+
+  group('snapAnchor', () {
+    final mono = PieceLibrary.byId('mono');
+    final line5h = PieceLibrary.byId('line5_h');
+
+    test('rounds to the nearest cell', () {
+      expect(geo.snapAnchor(mono, const Offset(78, 122)), (2, 3));
+      expect(geo.snapAnchor(mono, const Offset(99, 99)), (2, 2));
+    });
+
+    test('clamps so the piece bounding box stays on the board', () {
+      // line5_h is 5 wide: anchor x can be at most 3.
+      expect(geo.snapAnchor(line5h, const Offset(310, 0)), (3, 0));
+      expect(geo.snapAnchor(line5h, const Offset(-50, -50)), (0, 0));
+    });
+  });
+}

test/ui/game_screen_test.dart

@@ -0,0 +1,116 @@
+import 'package:block_seasons/core/rng.dart';
+import 'package:block_seasons/game/engine/piece_generator.dart';
+import 'package:block_seasons/game/models/piece_library.dart';
+import 'package:block_seasons/game/models/stage.dart';
+import 'package:block_seasons/l10n/gen/app_localizations.dart';
+import 'package:block_seasons/state/providers.dart';
+import 'package:block_seasons/ui/screens/game_screen.dart';
+import 'package:block_seasons/ui/widgets/board_widget.dart';
+import 'package:block_seasons/ui/widgets/piece_painter.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+final _stage = StageConfig.fromJson({
+  'id': 'drag_stage',
+  'seed': 11,
+  'moveLimit': 20,
+  'preset': const <Map<String, dynamic>>[],
+  'objectives': [
+    {'type': 'reachScore', 'target': 999999},
+  ],
+  'stars': {
+    'two': {'movesLeft': 5},
+    'three': {'movesLeft': 10},
+  },
+  'generatorProfile': 'mid',
+});
+
+PieceGenerator _smallPool() => PieceGenerator(
+      SeededRng(3),
+      pool: [
+        PieceLibrary.byId('mono'),
+        PieceLibrary.byId('domino_h'),
+        PieceLibrary.byId('domino_v'),
+      ],
+    );
+
+void main() {
+  testWidgets('dragging a tray piece onto the board places it',
+      (tester) async {
+    final container = ProviderContainer();
+    addTearDown(container.dispose);
+    container
+        .read(gameSessionProvider.notifier)
+        .startStage(_stage, generator: _smallPool());
+
+    await tester.pumpWidget(
+      UncontrolledProviderScope(
+        container: container,
+        child: const MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: GameScreen(),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    final view0 = container.read(gameSessionProvider)!;
+    final monoIndex = view0.tray.indexWhere((p) => p.id == 'mono');
+    expect(monoIndex, greaterThanOrEqualTo(0));
+
+    final boardRect = tester.getRect(find.byType(BoardWidget));
+    final cell = boardRect.width / 8;
+
+    // The dragged piece floats 70px above the finger, so aim the finger
+    // below the intended landing cell (0, 0).
+    final targetCenter = boardRect.topLeft + Offset(cell * 0.5, cell * 0.5);
+    final fingerEnd = targetCenter + Offset(0, 70 + cell / 2);
+
+    final start = tester.getCenter(find.byType(PieceWidget).at(monoIndex));
+    final gesture = await tester.startGesture(start);
+    await gesture.moveBy(const Offset(0, -30));
+    await tester.pump();
+    await gesture.moveTo(fingerEnd);
+    await tester.pump();
+    await gesture.up();
+    await tester.pumpAndSettle();
+
+    final view = container.read(gameSessionProvider)!;
+    expect(view.grid.isOccupied(0, 0), isTrue,
+        reason: 'mono should land on (0,0)');
+    expect(view.tray, hasLength(2));
+    expect(view.score, 1);
+  });
+
+  testWidgets('result overlay appears when out of moves', (tester) async {
+    final container = ProviderContainer();
+    addTearDown(container.dispose);
+    final oneMove = StageConfig.fromJson({
+      ..._stage.toJson(),
+      'moveLimit': 1,
+    });
+    container
+        .read(gameSessionProvider.notifier)
+        .startStage(oneMove, generator: _smallPool());
+
+    await tester.pumpWidget(
+      UncontrolledProviderScope(
+        container: container,
+        child: const MaterialApp(
+          localizationsDelegates: AppLocalizations.localizationsDelegates,
+          supportedLocales: AppLocalizations.supportedLocales,
+          home: GameScreen(),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    container.read(gameSessionProvider.notifier).tryPlace(0, 0, 0);
+    await tester.pumpAndSettle();
+
+    expect(find.text('Out of moves'), findsOneWidget);
+    expect(find.text('+5 moves (ad)'), findsOneWidget);
+  });
+}