Set up Express server and MongoDB connection

[Shalini828]

Summary

This PR sets up the backend server with MongoDB integration and adds the initial backend structure.

Changes Made

• Configured Express server
• Connected MongoDB using Mongoose
• Added dotenv configuration
• Enabled CORS and JSON middleware
• Added authentication routes
• Added inquiry routes
• Implemented database connection error handling
• Improved server startup handling

Testing

• Backend server starts successfully
• MongoDB connection verified
• Authentication routes tested
• Inquiry routes tested
• No syntax or runtime errors

fixes #132