Improvements : OAuth2 best practice & Frontend refactor

There are several improvements:

OAuth2 Best Practices:

• The access_token should only be stored in memory (not in localStorage).
• The refresh_token should be stored in HttpOnly cookies (not normal cookies).

Frontend Refactor:

• Pinia is recommended for Vue3 projects, not VueX.
• Use composition API instead of option API in Vue3.
• Use data provider pattern to improve maintenance.

TODO Feature:

• kubernetes deployment.