Render the new `semantic` block from the admin catalog-search status
endpoint in the Search Settings page: semantic readiness (with
disabled reason), overall vector coverage %, coverage-updated
timestamp, embedder capability, and a compact per-type coverage list.
Reuses the existing StatusRow/FieldGroup/Badge patterns and adds a
formatPercent helper; keeps the existing Vectorized Documents row.
The TS `semantic?` field is optional and the whole block is guarded so
a new frontend talking to an older backend during rollout degrades
gracefully.
Part of the hybrid-semantic-search hardening work (Task 8).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
