Ability to cancel an ongoing search

When the user searches for a package in a source tab, the GUI blocks the user from doing anything else (other than close ChocolateyGUI entirely).

The user should have the option to cancel the search.

Alternatively, the GUI should not block the user from interacting with the application, while the search is executed in the background.

Start by tracing the GUI's package-search flow and identify where the interface becomes blocked while a source-tab search runs. Compare the two requested outcomes: an explicit cancellation option or continued interaction during a background search. Done means the selected behavior works reliably without requiring the application to close.

Written by the indexing model from the issue text.