fix: backend-side search and filtering for AI systems

[Pcmhacker-piro]

Summary

Closes #678

This PR moves the searching and filtering logic for the AI systems registry from client-side to the backend. It introduces optional `search`, `risk_level`, and `compliance_status`

query parameters to the backend /api/v1/ai-systems/ list endpoint, updates the frontend API client/page to pass these parameters to the API call, and includes searchTerm in React
Query's queryKey to ensure proper cache invalidation and refetching.

## Type of Change

- [x] Bug fix
- [ ] New feature
- [ ] Documentation update
- [ ] Refactor
- [x] Tests
- [ ] Infra / CI

## Checklist

- [x] I have read [CONTRIBUTING.md](../CONTRIBUTING.md)
- [x] My code follows the project style (PEP 8 for Python, ESLint for TS)
- [x] I have added/updated tests where relevant
- [x] `pytest backend/tests/` passes locally
- [x] I have not committed `.env` or any secrets
- [x] I have updated documentation if needed

## Screenshots (if UI change)

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[Pcmhacker-piro]

hii @SdSarthak

the checks have passed. Could you please review and approve the pending workflows when you have a chance? Thank you!