fix(reader): harden swipe/long-press coexistence and next-chapter prefetch

- A long-press now cancels any pending swipe, so a hold-then-drag gesture
  opens the action sheet without also turning the page (regression-tested).
- The next-chapter prefetch no longer retries on every page flip when the
  endpoint fails (guard clears only when the next chapter changes), and it
  clears a previous chapter's warmed images on navigation so stale hidden
  <img>s don't linger.
- Tap zones set touch-action: pan-y so vertical panning stays native while
  horizontal swipes reach our handler.

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

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.104.0",
+  "version": "0.105.0",
   "private": true,
   "type": "module",
   "scripts": {