fix: correct navbar active state for login and signup routes

[kanaklatwal]

📌 Description

Fixed the navbar active state issue where the Signup button remained highlighted regardless of the current route.

The issue was caused because Login and Signup were using Link instead of NavLink, which prevented route-based active styling. Updated the implementation to use active route detection and corrected inactive styling behavior.

🔗 Related Issue

Closes #768

🛠 Changes Made

• Replaced Link with NavLink for Login and Signup buttons
• Added route-based active styling using isActive
• Fixed inactive button styling so only the current route is highlighted
• Tested behavior on /login and /signup

📸 Screenshots (if applicable)

Verified:

• /login → only Login highlighted
• /signup → only Signup highlighted

✅ Checklist

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

🚀 Notes for Reviewers

Please review the active state behavior for authentication routes and confirm UI consistency.