Add tests for jobMatching filter edge cases

[RUKAYAT-CODER]

Background

Filter-combination edge cases (empty, conflicting and overlapping filters) are untested. Add coverage.

Files to modify (2-3)

src/lib/jobMatchingFilters.ts
src/hooks/useAdvancedSearch.tsx

Acceptance Criteria

Implemented across the listed files

Unit/integration tests added or updated and passing

No regression; follows project coding standards