Implement API rate limiter

NestJS has a [rate limiting](https://docs.nestjs.com/security/rate-limiting#rate-limiting) module. We should implement it for security purposes!

The issue references the NestJS rate limiting module documentation. Start by reading that documentation to understand the module's setup and configuration. Look for existing security or middleware modules in the codebase to see where rate limiting should be integrated. Test the implementation by simulating API requests to ensure limits are enforced.

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