fix(security): remove plaintext password storage from client authentication

[Akshu121796]

Summary

Closes #81

• Linked the issue addressed by this PR
• Targeted the correct base branch
• Kept the changes scoped to a single issue
• No UI screenshots required
• Manually tested

What changed

• Removed the client-side dependency on registeredPassword stored in localStorage.
• Eliminated plaintext password retrieval and comparison from the login flow.
• Updated the authentication flow to rely on the existing backend /api/auth/login endpoint.
• Preserved the existing OTP verification and session handling after successful authentication.

Why this change is needed

Storing plaintext passwords in localStorage exposes sensitive credentials to XSS attacks and local browser access. This change removes that security risk by delegating credential validation to the backend while maintaining the existing user experience.

Testing

• Not tested
• Manually tested
• Added/updated automated tests

Manual verification:

• Registered password is no longer stored in localStorage.
• Login succeeds through the backend authentication endpoint.
• Invalid credentials are rejected.
• OTP flow and session creation continue to work as expected.

Screenshots

N/A (security/backend change)

[Akshu121796]

Heyy @jaideep005 ,
I have worked on issue #81
Please review it
If no changes , add the required labels, so it adds points to my profile
-type:security
-type:bug
-gssoc:approved
-backend (if available)

Thakyou so much for your support!!