Add error messages on student login

[iamrohitsuthar]

When students attempt to log in, the current implementation lacks proper error messaging. The following improvements are needed:

Invalid Roll Number or Password:
If students enter an incorrect roll number or password, the system should display a clear error message to indicate that the credentials provided are invalid. This will help students identify and correct their login information.

Student Has Already Submitted the Test:
In cases where a student has already submitted the test and attempts to log in again, the system should display an appropriate error message. This message should inform the student that multiple test submissions are not allowed.

[kedhar0608]

Hey I have worked on such issues earlier. I want to contribute to this. Let me work with you

[kedhar0608]

assign this to me