Fixed the Sign Up UI of the website

[Shayan-Bhowmik]

📌 Description

Fixed the sign-up form styling so the "Full Name" input now has the same visible background and border treatment as the Email and Password fields.

🔗 Related Issue

Closes #1149

🛠 Changes Made

• Restored the shared input-modern styling utility in the frontend stylesheet.
• Added consistent background, border, text, placeholder, and focus states for auth inputs.
• Ensured the Name field on the Create Account card renders with a visible text box boundary again.

✅ Checklist

• Code runs locally
• Followed project structure
• No console errors
• Properly tested changes
• Linked the issue

🚀 Notes for Reviewers

The fix is centralized in the shared input utility, so the signup form now stays consistent with the login form and any other inputs using the same class.