Keyboard Manager: Add app search when creating an "Open app" remap

### Description of the new feature / enhancement

Currently, Keyboard Manager only allows selecting an executable path for the Open app action. It would be helpful to also provide an option to search for and select an installed application directly.

### Scenario when this would be used?

Some apps, such as Windows Terminal, do not make their executable path obvious to the user. Adding an app search option would make it easier to create key remaps for these apps without manually locating the executable.

### Supporting information

_No response_

Start with the Keyboard Manager flow for creating an “Open app” remap and identify how executable paths are currently selected. Define the installed-application search source and selection behavior, then verify that apps such as Windows Terminal can be selected without manually locating an executable.

Written by the indexing model from the issue text.