🛡️ Sentinel: [HIGH] Enable Rate Limiting & Fix Dependency

[google-labs-jules]

• 🚨 Severity: HIGH
• 💡 Vulnerability:
  1. Rate limiting was disabled (commented out), leaving the API vulnerable to DoS and brute-force attacks.
  2. Application was crashing on startup due to @fastify/jwt v10 incompatibility with Fastify v4 (requires v5).
• 🎯 Impact: Potential service unavailability and lack of protection against abusive traffic.
• 🔧 Fix:
  1. Enabled rate limiting in backend/src/app.ts and fixed the error response to correctly propagate 429 status code.
  2. Downgraded @fastify/jwt to ^8.0.0 to match installed Fastify v4 version.
  3. Added jest.config.js, jest.setup.js and a regression test backend/src/__tests__/rate_limit.test.ts.
• ✅ Verification: Run npm test in backend/ directory. The new test verifies that 429 status code is returned after exceeding the limit.

---

PR created automatically by Jules for task 7539558591550902353 started by @Magnopiro-oficial

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.