List read-only import/export readiness contracts

Returns Phase 0 import/export readiness contracts for all platform launch verticals when the authenticated automation client has platform.import_export_readiness.read. External URL: /v1/providers/current/import-export-readiness. Current Next.js implementation path: /api/platform/v1/providers/current/import-export-readiness. This read-only route does not require Idempotency-Key; it exposes preview, validation, dedupe, rollback, export, offboarding, audit readiness posture, blocked execution gates, and a redacted service-role ledger summary only. It never confirms imports, writes database rows, returns raw uploaded files, returns source batch keys, creates export downloads, executes rollback or offboarding actions, exposes private source evidence, or calls external providers.