[hojjatabdollahi]

This pulls in gallery mode and large image decode offloading from cosmic-files, and the image cache from #456. Image cache is limited to 250mb max (from @FreddyFunk's PR), I only changed the cache-key to take app version into account.

• you can enlarge an image by clicking on it (gallery view)
• caches the images, so it's faster next time
• caches using image url and app version, so refetches images on app update
• removed the next/prev buttons if there's only one image

recording-2026-07-15_12-52-11-trimmed.mp4

This looks like a big PR, but it's mostly either from cosmic-files, or from Freddy's PR.

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[jklgrasso]

Please resolve the conflicts when you're able

[hojjatabdollahi]

@jklgrasso done

[jklgrasso]

Regression testing passed

## Checklist

• Able to install & remove a Flatpak app.
• Able to install & remove a Deb app.
• Able to install Deb updates.
• Searching still works.
• Browsing categories still works.
• Able to remove & re-add Flatpak sources.