fix(reader): suppress Android image callout freezing the image viewer (#4425)

Long-pressing an image in the zoom viewer on Android triggers the
WebView's native image callout (context menu / drag / magnifier) at the
same time as the viewer's own pinch/pan/zoom touch handlers, locking up
the whole app until restart. Same root cause as the book-cover freeze
(PR #4345): `-webkit-touch-callout: none` doesn't inherit, so the class
must sit on an ancestor of the `<img>`.

Apply the existing `.no-context-menu` class to the viewer container so
the `.no-context-menu img` rule reaches the zoomed image and disables
the native callout. Harmless on desktop (the property is a no-op there
and right-click-save still works).

Closes #4420

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

apps/readest-app/src/__tests__/components/ImageViewer.test.tsx

@@ -0,0 +1,39 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { render, cleanup } from '@testing-library/react';
+
+import ImageViewer from '@/app/reader/components/ImageViewer';
+
+vi.mock('@/hooks/useTranslation', () => ({
+  useTranslation: () => (s: string) => s,
+}));
+
+// useKeyDownActions pulls in EnvContext + device store; not under test here.
+vi.mock('@/hooks/useKeyDownActions', () => ({
+  useKeyDownActions: () => {},
+}));
+
+// ZoomControls reaches into the theme store and Tauri window APIs; stub it out.
+vi.mock('@/app/reader/components/ZoomControls', () => ({
+  __esModule: true,
+  default: () => null,
+}));
+
+afterEach(cleanup);
+
+const gridInsets = { top: 0, right: 0, bottom: 0, left: 0 };
+
+describe('ImageViewer', () => {
+  it('suppresses the native image callout on the zoomed image', () => {
+    // The WebView's native long-press image callout collides with the
+    // viewer's own pinch/pan handlers on Android and freezes the app. The
+    // zoomed <img> must live under a `.no-context-menu` ancestor so the
+    // global `.no-context-menu img { -webkit-touch-callout: none }` rule
+    // disables that callout. Mirrors the book-cover fix (PR #4345).
+    const { container } = render(
+      <ImageViewer src='blob:test-image' onClose={vi.fn()} gridInsets={gridInsets} />,
+    );
+
+    const calloutSafeImage = container.querySelector('.no-context-menu img');
+    expect(calloutSafeImage).toBeTruthy();
+  });
+});

apps/readest-app/src/app/reader/components/ImageViewer.tsx

@@ -367,12 +367,15 @@ const ImageViewer: React.FC<ImageViewerProps> = ({
   if (!src) return null;
 
   return (
+    // `no-context-menu` suppresses the WebView's native long-press image
+    // callout (via the `.no-context-menu img` rule). On Android it otherwise
+    // collides with the pinch/pan handlers below and freezes the app.
     <div
       ref={containerRef}
       tabIndex={-1}
       role='button'
       aria-label={_('Image viewer')}
-      className='fixed inset-0 z-50 flex items-center justify-center outline-none'
+      className='no-context-menu fixed inset-0 z-50 flex items-center justify-center outline-none'
       onKeyDown={handleKeyDown}
       onWheel={handleWheel}
       onTouchMove={onTouchMove}