Consolidate URL and Token Fields into a Single Input Field

Summary:
Currently, when adding a new instance to the Defguard desktop client, users must copy and paste two separate values: the instance URL and the authentication token. This is unnecessarily complex and introduces room for error.

Proposal:
Introduce a single input field in the desktop client that accepts a combined string containing both the URL and the token (e.g., https://example.defguard.com# or some base64 altogether). This would simplify the process for desktop users, similar to how mobile users benefit from scanning a QR code.

Benefits:
- Simplifies onboarding for desktop users
- Eliminates confusion or mistakes when copying two fields
- Enables easy sharing of full connection strings in documentation or web UI
- Aligns with the streamlined QR code experience already available on mobile