POST .../collections/{cid}/migrate — now safe to ship since all write paths
are sidecar-aware. Idempotent, one commit per collection.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Direct-commit to the sidecar (D7), contributor+ gated (INV-4), schema-validated
at the write boundary, lazy-migrates a legacy entry, re-ingests. GET RFC now
returns the per-entry meta mapping and a can_edit_meta capability.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>