Photo backup: bug fixes and improvements (PRs #54, #55, #56) #57

Hi! I started using SyncUp and it's been great overall, but while relying on the photo-backup feature I ran into a few bugs and rough edges. I used Claude to put together quick fixes and some improvements, and I've been running a build with all three PRs applied for a while now — it works well for me day to day.

To be clear: I'm not asking you to merge these as-is. Even if they don't fit the project, feel free to use them as a reference / code example for how the fixes could be approached.

Splitting the work into focused PRs so they're easier to review and merge independently:

• fix: route photo-backup into configured folders and skip overlapping sources #54 — fix: route photo-backup into configured folders and skip overlapping sources
  Backup couldn't write into SAF folders or All-Files-Access folders outside foldersRoot, and the overlap guard missed nested assets (e.g. DCIM/Archive got re-copied into DCIM) because of /sdcard vs /storage/emulated/0 and slash differences. Both fixed.

• ui: unify the folder-location picker across add/accept flows #55 — ui: unify the folder-location picker across add/accept flows
  The three storage choices (app sandbox / device folder / SAF) were rendered with different controls in the add vs accept screens. Unified into one FolderLocationPicker (uniform radio cards). Independent of the other two.

• feat: background photo backup + move, keep-name, by-album options #56 — feat: background photo backup + move, keep-name, by-album options
  Periodic background backup (Hourly / 6h / Daily), move-instead-of-copy, keep-original-filename toggle, and a by-album folder structure. Stacked on fix: route photo-backup into configured folders and skip overlapping sources #54 (shares PhotoBackup.ts); I'll rebase onto master once fix: route photo-backup into configured folders and skip overlapping sources #54 lands.

Happy to adjust any of these to fit your preferences — squash, split further, reword, whatever works best for the project.