Add contributor dashboard with backend JSON persistence

[khushiiii4]

Description

Added a full contributor dashboard feature with form submission and backend JSON persistence.

🔹 Created dashboard.html page to display contributor cards dynamically
🔹 Built backend using Node.js + Express
🔹 Added /contributors GET & POST REST API routes
🔹 Created contributors.json to store data persistently
🔹 Integrated frontend form with backend using Fetch API
🔹 Updated dashboard.js to load, display, and add contributors in real-time

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist:

• I have made this from my own understanding
• I have taken help from some online resources
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in important areas
• My changes generate no new warnings
• The title of my pull request describes the changes clearly

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[khushiiii4]

Hi, I have submitted the Contributor Dashboard feature. Please review it when possible 😊

[khushiiii4]

Hi, maintainers
I have completed the requested changes. Please review when you get time.
Looking forward to your feedback and approval. Thank you!