[Feature] Add setting to make timeline scrubber permanently visible on mobile

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

• Yes

The feature

When I set up an album for my grandma and showed how to use Immich, I noticed that she couldn’t use the timeline scrubber / scroll thumb.

There were two concrete issues:
1. She failed to notice the icon's appearance.
2. She was too slow to drag it before it vanished again.

I believe the current design isn’t accessible for elderly people. Therefore, I propose adding an option that permanently displays the timeline scrubber on mobile devices.

Just to make sure it is clear which button I'm referring to:
<img width="590" height="1278" alt="immich_scrubber" src=" />


Platform

• Server
• Web
• Mobile