fix(frontend): rebuild swiper after single-image delete

[lstein]

Summary

• Single-image delete (control panel trash button) patched one slide and adjusted slideState in place, leaving neighbor slides with stale dataset.globalIndex values after the backend re-indexed.
• After a few deletes, scrolling forward hit a slide whose stale index made resolveOffset wrap to 0 before the real last image was ever appended — the very last image of the album became unreachable.
• Replaces the surgical patching in handleSuccessfulDelete with a full state.single_swiper.resetAllSlides() rebuild (matching the bookmark-delete path), and clamps currentGlobalIndex so deleting the last image lands on the new last image.

Positioning behaviour after delete:

• Deleting the current image keeps currentGlobalIndex unchanged — the backend re-index slides the next image into that slot.
• Deleting the last image clamps down to the new last.
• Deleting the only image leaves an empty swiper.
• In search mode: splice the result, decrement subsequent .index values, clamp currentSearchIndex so the next result fills the slot; exit search mode if results become empty.

Test plan

• Delete a middle image — current position stays, next image appears in its slot.
• Delete the last image (highest index) — lands on the new last image.
• Delete the only image in an album — swiper is empty.
• In search mode, delete the current result — advances to next result; on last result, falls back to the new last.
• After several deletes, scroll to the chronological end — the real last image is reachable.