feat(reader): swipe to turn pages on touch devices

[ajslater]

Summary

• Add left/right swipe gestures to the horizontal comic reader on touch devices, mirroring the existing ArrowRight/ArrowLeft keyboard behavior.
• Implemented by overriding v-window's built-in touch prop with handlers that call routeToDirection. Vuetify's touch directive already lives on that element — the defaults try to flip between v-window items, which are disabled here and rely on URL routing instead.
• RTL handling is automatic: routeToDirection normalizes the direction through normalizeDirection, so manga / right-to-left books swap left/right just like the arrow keys do.
• Vertical reader mode is untouched — it already responds to native touch scrolling.

Notes for reviewer

• This branch was already 2 commits ahead of develop before this change: the v1.12.3 version bump + news, and a merge from develop. Those commits are unrelated to the swipe feature and just rode along on this branch.
• NEWS.md was not modified for the swipe feature; happy to add a bullet under v1.12.3 if you'd like.

Test plan

• Open a comic in horizontal mode on a phone / tablet — swipe left advances a page, swipe right goes back.
• Open an RTL / manga title — swipe directions are flipped (left = previous, right = next), matching the arrow keys in RTL.
• In Chrome devtools, toggle device toolbar (Cmd-Opt-I → device icon) and confirm swipes register at the default 16px threshold.
• Two-page mode swipes still advance by a spread (delegated to the existing route logic).
• Vertical reading mode is unaffected — native scroll still works, no horizontal swipe interference.

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