Preview a records connector before connecting

With the config and credential about to be connected, list one page per chosen entity at the live vendor and show what the mapping makes of the first records — the facts, the relations, the fields left unmapped, the drops by name. Nothing is written. Records (docs/roadmap/crm-sources-2026-09.md): a CRM row enters as FACTS — its mapped attributes become deterministic candidates under the record’s own id, never prose a model re-extracts. Source plane operator surface (docs/roadmap/raw-evidence-sources-2026-09.md) — answers a bare 404 until SOURCE_PLANE_ENABLED=1.

Required scope: brain:admin.