feat(reader): open image gallery & table zoom on single tap

[chrox]

What & why

Today the image gallery (ImageViewer) and table zoom (TableViewer) can only
be opened by long-pressing the image / table. This adds a second, equivalent
way in: in reflowable EPUBs, a single tap on an image or table opens the
same viewer. Long-press is unchanged and keeps working everywhere.

This is motivated by #4584, where single taps stop registering after using
picture zoom on some Android WebView builds (long-press still works). Rather than
chase that elusive, WebView-version-specific root cause, this makes the feature
reachable by both gestures so users aren't dependent on a single input path.

Behavior

• Reflowable EPUB — tap an <img> / <svg>-with-<image> opens the image
  gallery; tap a <table> opens the table zoom.
• Fixed-layout (PDF / comics / manga) — unchanged: a tap still turns the page
  (there the tap is the page-turn gesture).
• Long-press — unchanged in all book types.
• Linked image (image inside <a>) — unchanged: the tap follows the link.
• Drag / long-hold / double-tap — unchanged: the new branch sits after the
  existing link/footnote/drag/long-hold/Word-Wise guards and rides the 250ms
  double-click deferral, so it can't double-trigger.

Implementation

• Reuses the existing iframe-long-press → useLongPressEvent →
  handleImagePress / handleTablePress flow; no new message type or consumer.
• New shared detectMediaTarget() helper resolves an element to the viewer
  payload; both the long-press path and the new tap path use it so they can't
  drift.
• handleClick gains an isFixedLayout flag (passed from FoliateViewer via
  bookData.isFixedLayout) to gate the tap-to-open branch.

Testing

• pnpm test — full suite green (5644 passed). New cases in
  iframeEventHandlers.test.ts: reflowable image-tap and table-tap post
  iframe-long-press; fixed-layout image-tap still posts iframe-single-click;
  linked-image tap posts neither; existing double-click / long-hold tests pass.
• pnpm lint (tsgo + biome) — clean.

Note: this does not claim to fix the underlying #4584 tap-death (unreproduced,
likely WebView-148-specific); it gives an independent entry path.

🤖 Generated with Claude Code