[MainUI] Rework uninstalling addons from ` /usr/share/openhab/addons`

[dilyanpalauzov]

With OpenHAB 5.0.1 I put under /usr/share/openhab/addons the file https://github.com/dilyanpalauzov/openhab-addons/releases/download/5.0.x_binding_mini2/org.openhab.binding.mini2-5.0.2-SNAPSHOT.jar and change its permissions to openhab:openhab. In MainUi under /addons I select to uninstall “Minimal Binding bundle with logging ”, then openhab.log gets:

2025-09-08 10:23:05.517 [ERROR] [t.core.internal.addons.AddonResource] - Exception while uninstalling add-on: null

• In MainUI, either there should be instead of an option to unstall addons from /usr/share/openhab/addons text about this, or the addon should be removed, or there should be some more meaningful error presented to the user. Exception: null is not meaningful enough.