feat(ui): migrate context visualizer to kit-ui primitives

- Re-enable full kit-ui-check over src (remove context exclusion script)
- Wrap context panels in Card; use EmptyState for loading/error/unknown states
- Normalize spacing gaps to var(--space-N) tokens across context components
- Rename summary header classes to avoid hand-rolled-top-bar false positives

Author: diazMelgarejo