[Bug] Imported private key is cleared when returning from the agent harness setup screen

[AIQAEngineer]

After importing a private key and continuing to the Set up your agent harnesses screen, clicking Back returns to the private-key screen with an empty input. The previously entered key is no longer populated.

To Reproduce:

1. Open the Buzz onboarding flow.
2. Click Use an existing key.
3. Enter a valid private key.
4. Continue to Set up your agent harnesses.
5. Click Back.
6. Notice that the private-key input is empty.

Expected behavior:
The previously entered private key should remain populated and masked when the user returns to the private-key screen.

Environment (please complete the following information):

• OS: Windows