refactor: authentication flow

<!-- DO NOT IGNORE THE TEMPLATE! Thank you for contributing! Before submitting the PR, please make sure you do the following: - Read the [Contributing Guide](https://github.com/antfu/contribute). - Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate. - Provide a description in this PR that addresses **what** the PR is solving, or reference the issue that it solves (e.g. `fixes #123`). - Ideally, include relevant tests that fail without this PR but pass with it. --> ### Description <!-- Please insert your description here and provide especially info about the "what" this PR is solving --> Do some refactoring for the authentication flow, but has no design for the sign-in screen https://github.com/user-attachments/assets/b157002a-25b5-41a7-9a44-e9d10d7dee18 ### Linked Issues ### Additional context <!-- e.g. is there anything you'd like reviewers to focus on? -->