fix(reader): zoom linked images on single tap (#4757)

[chrox]

Problem

Fixes #4757. In reflowable books, a single tap on an image wrapped in an <a> element followed the link instead of opening the image zoom viewer.

Root cause

postSingleClick in src/app/reader/utils/iframeEventHandlers.ts returned early for any element inside an anchor (element.closest('sup, a, audio, video')) before reaching the media-detection branch added in #4600. Long-press already opened the viewer for linked images (its listeners have no anchor skip), so single-tap was inconsistent.

Fix

Compute the media target up front and let it bypass the anchor guard, so a tapped img / svg-with-image / table opens the viewer just like long-press:

const footnote = element?.closest(footnoteSelector);
const media = !isFixedLayout && !footnote ? detectMediaTarget(element) : null;
if (!media && element?.closest('sup, a, audio, video') && !element?.closest('a.duokan-footnote:not([href])')) {
  return;
}

Decision order is unchanged otherwise: footnote container class wins (forces media to null, so footnote markers rendered as images still show the popup), then image/table zooms, then link navigates, then page turns. The later dispatch reuses the same media value (no second detectMediaTarget call).

Behavior

• Reflowable + linked image -> opens the viewer (the fix)
• Reflowable + footnote-link image -> footnote popup/navigation preserved
• Plain text links, bare images, tables, fixed-layout tap-to-turn, and drag/long-hold guards -> unchanged

Tests

Updated src/__tests__/reader/utils/iframeEventHandlers.test.ts: the linked-image case now asserts iframe-open-media, plus a new footnote-link-image guard test confirming footnotes are excluded. Full pnpm test and pnpm lint pass.

🤖 Generated with Claude Code