Factor cache-on-save's renumberPhotos into a shared PhotoRenumberer class
(Grav\Plugin\Shared), the single owner of the photo-NN naming invariant used
by both the create/edit reconcile and the upcoming live reorder route, so their
numbering can't diverge.
Changes vs the old private method:
- Zero-pads to photo-01..NN (pad width grows with the set) so lexicographic
media order equals numeric order past 9 photos — cover = images|first stays
correct for 10+ photos. Normalises pre-existing un-padded photo-N on first pass.
- Image-extension guard moved into the helper: only real image files on disk are
renamed, so a crafted manifest naming the entry .md, a .gpx or a .meta.yaml is
skipped by every caller, not just cache-on-save.
Create-mode entries now also emit photo-01..NN — an intentional, accepted side
effect of sharing one helper.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
