[Feature] Add smooth timeline scrubbing toggle

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request.

• Yes

The feature

Currently, the timeline scrubber on mobile is smooth on timelines with less than 12 months, and snaps to the grid sections (days or months) otherwise. I much prefer the smooth behavior, even on large libraries, so I'd like a setting to use it everywhere.

Proposal: a "Smooth timeline scrubbing" switch in Settings > Photo Grid, off by default so nothing changes for anyone else. The scrubber already has a non-snapping mode (used for short timelines and on the search page), so this only reuses it.

I already have this working and tested on iOS against a v3.3.3 server. If it's something you'd accept, I'll open a PR.

Platform

• Server
• Web
• Mobile