Potential fix for code scanning alert no. 5: Missing rate limiting

[Tanker187]

Potential fix for https://github.com/Tanker187/vite/security/code-scanning/5

To fix the problem, we should introduce a rate-limiting middleware for incoming HTTP requests before they reach the expensive handler that uses fs.readFileSync. A well-established library such as express-rate-limit can be used to enforce limits on how many requests a client can make within a given time window. This mitigates DoS risks without otherwise changing the application’s behavior.

Concretely, in playground/css-lightningcss-proxy/server.js, we should:

1. Import express-rate-limit alongside the existing imports.
2. Define a rate limiter instance (for example, limiting a single IP to a certain number of requests per time window, such as 100 per 15 minutes).
3. Register this limiter with app.use(...) before the wildcard route app.use('*all', async (req, res, next) => { ... }), so that all requests (or at least those that hit this handler) are subject to rate limiting.
4. Keep the rest of the logic (including Vite middleware and file reading) unchanged.

This approach preserves existing functionality while adding protection against abusive request patterns.

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