[Feature] Add "Select All" option for bulk download 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

PR #18878 added bulk download to the mobile app, which is great — but you still have to tap each photo/video individually before hitting the download button. For large albums or library-wide downloads, this is tedious and impractical.

Request: Add a "Select All" button (or long-press → "Select All" context option) in multi-select mode so users can download everything in the current view (album, folder, search results) in one go.

This would bring the mobile experience in line with the web UI, where Ctrl+A already works for selecting all visible assets.

Platform

• Server
• Web
• Mobile