Implement UI Tests

[jsattler]

Create UI tests to verify the user interface and user flows using XCTest.

Scope & Ideas:

• Settings Navigation: Verify the Settings window opens and tabs are navigable.
• Settings Interaction:
  • Verify changing the Codec updates the UI (e.g., enables/disables Alpha Channel toggle).
  • Verify the 'Start Recording' button state changes based on content selection (if mockable).
• Recording Flow:
  • Test the 'Stop Recording' button availability during a session.
  • Verify timer updates in the menu bar.
• Permissions: Verify proper alert dialogs are shown when permissions are denied (using launch arguments to mock state if possible).