Potential fix for code scanning alert no. 1: Missing rate limiting

[balajidharma]

Potential fix for https://github.com/balajidharma/node-express-hub/security/code-scanning/1

To fix the missing rate limiting, we should add a rate-limiting middleware to the /protected route. The best way to do this is to use a well-known package such as express-rate-limit. We will import express-rate-limit, define a rate limiter (e.g., allowing 100 requests per 15 minutes per IP), and apply it specifically to the /protected route. This approach avoids changing the behavior of other routes and does not interfere with existing functionality.

Steps:

• Import express-rate-limit at the top of the file.
• Define a rate limiter instance with reasonable defaults.
• Add the rate limiter as middleware to the /protected route (before verifyToken).
• No changes to other routes or logic.

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