update Institute domain

[Harshbansal8705]

Update institute domain to kgpian.iitkgp.ac.in in src/controllers/user.ts:

        const { email, password } = parseResult.data;
        if (!email.endsWith("@iitkgp.ac.in")) {
            return res.status(400).json({
                message: "Email must end with @iitkgp.ac.in",