Improve GitHub installation handling and add UI error boundary

Added an ErrorBoundary to the project creation wizard — A new ErrorBoundary component now wraps the Project Creation Wizard to catch rendering errors and show a readable error card with a retry option, preventing blank screens during project setup.
Claimed orphaned GitHub installations during onboarding — When a user had no linked installations, the system now claims previously unowned GitHub installations (created without a browser session) and associates them with the first authenticated user who visits the project creation flow.

Added an ErrorBoundary component and used it on the New Project page to catch rendering errors in the Project Creation Wizard and display a clear error card with a retry option.frontend

Updated the GitHub installations GET handler to claim orphaned installations when no installations were found for a user, improving reliability of the onboarding flow.backend
Added a claimUnclaimed database method to assign previously unowned GitHub installations to the visiting user, addressing installs created without a browser session.database
Added error logging to the onboarding API to make failures easier to diagnose.backend