fix(auth): persist updated refresh_token and refresh_expires_at on token refresh

[bwebs]

Summary

Fixes an issue where renewing or refreshing tokens did not update or save refresh_token and refresh_expires_at in the database.

Changes

• In CurrentAuth.set_token() (lkr/auth_service.py), updated the SQL UPDATE auth statement to persist refresh_token and refresh_expires_at alongside access_token and token_type.
• Updated in-memory properties on CurrentAuth when a new refresh_token is present.
• Added tests in tests/test_oauth_account.py verifying that refresh_token is updated in SQLite after token refresh.

Fixes #41

[gemini-code-assist]

Code Review

This pull request updates the token storage logic in auth_service.py to persist the refresh_token and its expiration timestamp in the database, with corresponding updates to the test suite. The review feedback points out that refresh_expires_at should only be updated when a new refresh_token is actually returned, to avoid mismatching the server's actual token validity when the refresh token is not rotated.