[Request] Select the correct APK by signing key

### Guidelines

- [x] I have searched the issue tracker for [open](https://github.com/Droid-ify/client/issues) and [closed](https://github.com/Droid-ify/client/issues?q=is%3Aissue+is%3Aclosed) issues that are similar to the feature request I want to file, without success.
- [x] I'm not requesting app support for a specific repo — that's up to repo maintainers
- [x] I understand this might not get built (Droid-ify is maintained by a single person)

### Problem

I just ran into this with: https://f-droid.org/packages/juloo.keyboard2/

There are apparently now two APKs available, the one from the author had a different signing key. The UI presented a nice warning about that, thanks!

### Proposed solution

I'd very much like the software to figure this out and choose the correct signing key based on the already installed APK.

At the very least, it would help immensely if the version marked as installed included the fingerprint also.

### Extras

_No response_

Start by examining the UI that shows the installed version and the warning about differing signing keys, then trace how the app identifies the installed APK and presents available APKs. The request leaves open whether the goal is automatic selection, showing the installed APK's fingerprint, or both; clarify the expected behavior before estimating completion.

Written by the indexing model from the issue text.