feat: add detection builder UI

[valITino]

Summary

• extend API helpers with builder schema, compile, preview, and save endpoints
• add step-based Detection Builder page to craft and test rules
• wire Builder into frontend navigation and router

Testing

• pre-commit run --files frontend/src/lib/api.ts frontend/src/main.tsx frontend/src/pages/Builder.tsx
• npm test
• npx eslint src/lib/api.ts src/main.tsx src/pages/Builder.tsx -f json

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https://chatgpt.com/codex/tasks/task_e_689866f52ee0832dbd7d5fb6f9bf4a34