add ClideLightbox — click image cards to enlarge (T-252)

The inline image cards (T-249) are often too small to read. Clicking one now
opens a full-screen lightbox: zoom (scroll wheel / pinch), pan when zoomed,
double-click to reset to fit, Esc / close button / backdrop click to dismiss.

ClideLightbox is a reusable primitive (lib/widgets/) over Flutter's
InteractiveViewer with clide-owned zoom gestures, shown via the DialogRouter
(dimmed backdrop, single modal at a time, D-78). The card stays display-only;
the click is a navigation gesture, not an inline control.

CLI parity (D-6): `clide image show <path> --fullscreen` opens straight into
the lightbox instead of injecting a card.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/daemon/image_commands_test.dart

@@ -49,6 +49,14 @@ void main() {
     expect(published.single.data, {'path': '/abs/docs/diagram.png', 'caption': 'before the fix'});
   });
 
+  test('--fullscreen rides along in the payload (T-252)', () async {
+    wire();
+    final r = await show(['docs/diagram.png'], flags: {'fullscreen': true});
+    expect(r.ok, isTrue, reason: r.error?.message);
+    expect(r.data['fullscreen'], isTrue);
+    expect(published.single.data, {'path': '/abs/docs/diagram.png', 'fullscreen': true});
+  });
+
   test('accepts the documented formats case-insensitively', () async {
     for (final name in ['a.PNG', 'b.jpg', 'c.jpeg', 'd.gif', 'e.webp', 'f.bmp']) {
       wire(found: {name});

test/widgets/clide_lightbox_test.dart

@@ -0,0 +1,74 @@
+/// T-252: ClideLightbox — full-screen zoom/pan overlay primitive.
+library;
+
+import 'package:clide/widgets/widgets.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../helpers/kernel_fixture.dart';
+import '../helpers/widget_harness.dart';
+
+bool _textHas(Object? w, String s) => w is ClideText && w.data.contains(s);
+
+void main() {
+  late KernelFixture f;
+  setUp(() async => f = await KernelFixture.create());
+  tearDown(() => f.dispose());
+
+  Widget box(VoidCallback onDismiss) => MediaQuery(
+        data: const MediaQueryData(size: Size(800, 600)),
+        child: ClideLightbox(onDismiss: onDismiss, child: const SizedBox(width: 200, height: 150)),
+      );
+
+  testWidgets('renders the zoom hint and an InteractiveViewer', (tester) async {
+    await tester.pumpWidget(harness(f, box(() {})));
+    await tester.pumpAndSettle();
+    expect(find.byType(InteractiveViewer), findsOneWidget);
+    expect(find.byWidgetPredicate((w) => _textHas(w, 'Esc to close')), findsOneWidget);
+  });
+
+  testWidgets('Esc dismisses', (tester) async {
+    var dismissed = false;
+    await tester.pumpWidget(harness(f, box(() => dismissed = true)));
+    await tester.pumpAndSettle();
+    await tester.sendKeyEvent(LogicalKeyboardKey.escape);
+    await tester.pumpAndSettle();
+    expect(dismissed, isTrue);
+  });
+
+  testWidgets('the close button dismisses', (tester) async {
+    var dismissed = false;
+    await tester.pumpWidget(harness(f, box(() => dismissed = true)));
+    await tester.pumpAndSettle();
+    await tester.tap(find.ancestor(of: find.byType(ClideIcon), matching: find.byType(GestureDetector)));
+    await tester.pumpAndSettle();
+    expect(dismissed, isTrue);
+  });
+
+  testWidgets('double-tap resets without dismissing', (tester) async {
+    var dismissed = false;
+    await tester.pumpWidget(harness(f, box(() => dismissed = true)));
+    await tester.pumpAndSettle();
+    final viewer = find.byType(InteractiveViewer);
+    await tester.tap(viewer);
+    await tester.pump(const Duration(milliseconds: 50));
+    await tester.tap(viewer);
+    await tester.pumpAndSettle();
+    expect(dismissed, isFalse);
+    expect(find.byType(InteractiveViewer), findsOneWidget);
+  });
+
+  testWidgets('scroll wheel zooms in and out', (tester) async {
+    await tester.pumpWidget(harness(f, box(() {})));
+    await tester.pumpAndSettle();
+    final center = tester.getCenter(find.byType(InteractiveViewer));
+    final pointer = TestPointer(1, PointerDeviceKind.mouse)..hover(center);
+    await tester.sendEventToBinding(pointer.scroll(const Offset(0, -100))); // in
+    await tester.pumpAndSettle();
+    await tester.sendEventToBinding(pointer.scroll(const Offset(0, 100))); // out
+    await tester.pumpAndSettle();
+    expect(find.byType(InteractiveViewer), findsOneWidget);
+  });
+}