Implements 6 high-priority improvements from code review:
Backend:
- Make label business limits configurable via application.yml (max-definitions, max-per-skill)
Frontend:
- Split use-skill-queries.ts into domain-specific modules (label/namespace/user/skill)
- Enable @typescript/no-explicit-any as warning and clean up 10 any types
- Unify API error handling by removing unwrap() in favor of fetchJson()
Testing:
- Add label system scenarios to smoke test script
- Add 6 new tests for label management UI (validation, rendering)
All tests passing: 301 backend, 129 frontend
