feat(api): add per-user rate limiter on scan endpoints

[Tirthpanchori]

Description

Implements per-user rate limiting on the FreshScan AI backend to prevent abuse of the Hugging Face Space inference endpoint and Supabase resources.

What this PR does:

• Adds slowapi==0.1.9 middleware for request rate limiting
• Creates backend/rate_limiter.py with a get_user_id key function that keys limits by authenticated Supabase user ID, falling back to client IP for unauthenticated requests
• Applies a global default limit of 100 requests/hour across all endpoints
• Applies a stricter limit of 20 requests/minute on /api/v1/scan and /api/v1/scan-auto (the heavy ML inference endpoints)
• Returns clean JSON 429 Too Many Requests responses with retry_after field
• Adds a /api/v1/health endpoint for lightweight status checks
• Adds 5 tests in backend/tests/test_rate_limiter.py covering 429 behavior and response shape

Closes #4

Checklist

• npm run lint passes with no errors
• npm run build compiles without TypeScript errors
• python -m pytest passes (including new tests I added)
• No .env files, API keys, secrets, model weights, or __pycache__ in this diff
• Branch is rebased on main, not merged

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[jpdevhub]

backend test is failing fix that.

[Tirthpanchori]

backend test is failing fix that.

Fixed - added slowapi to requirements-base.txt and requirements-ci.txt so it's available in the CI environment. Latest commit 7a41d6e should resolve the ModuleNotFoundError.

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Project	Deployment	Actions	Updated (UTC)
fresh-scan-ai	Ready	Preview, Comment	Jun 7, 2026 4:17pm

[jpdevhub]

Thanks for contributing

[Tirthpanchori]

Thanks for contributing

Happy to contribute! Looking forward to more.