"Import Projects" button functionality can be found misleading

Steps to reproduce:

1. Open Unity Hub
2. Delete all projects from the Projects tab
3. Press the "Import projects" tab
   1. Select any project directory in the prompt, or
   2. Select any directory (except the parent directories) in the prompt
4. Press "Open"
5. Observe the Hub

Actual results: The directory is not added to the list and nothing indicates what went wrong

Expected results: Some information is displayed for what went wrong

Reproducible with versions: 3.18.0

Tested on (OS): Windows 11 Pro (25H2)

Notes:

• To make it clear what the button does, one of these should be expected:
  • A warning/error is thrown when an invalid directory is selected
  • A single selected project is parsed as a valid project to import
  • A tooltip is displayed when hovering over the 'Import Projects' button