Add Complete Comment Section (Frontend + Backend)

[Raaaaahil]

🧩 Summary

Added a complete comment system integrated with both frontend and backend.

🔧 Backend:

• Created Comment.model.js, comment.controller.js, and comment.routes.js
• Linked comments with posts and users using Mongoose.
• Integrated routes in main app file.

💻 Frontend:

• Built Comments.jsx component.
• Integrated with backend comment APIs.
• Added posting, deleting, and live-refresh features.
• Fixed text visibility in dark mode.

✅ Testing

• Verified comment posting, fetching, and deletion.
• Tested in both dark/light mode.
• Ensured user authentication before posting.

Closes #6