feat: Add user authentication

[datnguyen1]

Summary

Add user authentication so comics can be associated with users and access can be controlled.

Scope

• Backend: JWT-based auth (register, login, logout)
• Backend: Protect comic routes (create/update/delete require auth; list/detail can be public)
• Backend: Associate comics with author (user ID)
• Frontend: Login/register pages
• Frontend: Auth context or state (store token, user)
• Frontend: Guard create/edit routes; show "My Comics" vs public list
• Persist token (e.g. localStorage) and handle refresh/expiry

Notes

• Auth middleware and JWT_SECRET already exist in backend/src/middleware/auth.js but may need wiring.
• Comic model has author: ObjectId field.

[jainp2590]

Hi,
I’m interested in working on this issue. I have reviewed the description and would like to take it up.
Please assign it to me if possible. Thank you!

[datnguyen1]

Hi @jainp2590,

please feel free to submit a pull request. I will review