feat: Add "Use installed APK" button to APK availability dialog

[MarcaDian]

What's new

Added Use installed APK button in the APK selection dialog

When patching an app that is already installed on device as a regular (non-split) APK, Morphe now offers a shortcut button - Use installed APK (vX.Y.Z) - instead of requiring to manually locate and pick the file. Tapping it copies the installed APK to a temporary location and starts patching
automatically.

How it works:

• The button is available in expert mode only and appears when the installed app version is compatible with the selected patch bundle (respects the bundle's compatibleVersions field; universal patches always show it)
• If the installed app is already patched by Morphe (detected via certificate fingerprint), the button is hidden to avoid re-patching an already-patched build
• If a previously saved original APK of the same version already exists, only one button is shown to avoid duplicates
• For root users, the "original APK required" warning in the dialog is suppressed when the app is already installed, since root mount patching doesn't require re-installation
• The download instructions dialog also hides the "install the original first" step for root users when the app is already present

Patcher screen:

• When installation fails due to a package conflict (signature mismatch between patched and installed versions), a new warning badge now explains why the conflict occurred: "The patched app uses a different certificate than the installed version"