Spec cleanup: post-covenant rewrite of specs/relay/commongrid-nisc-matcher.md in mono

The v1.5 spec still references the now-dead private surface (commongrid.* schema, internal_api_consumer role, /api/internal/*). Rewrite as v1.6 describing the covenant-compliant public surface: POST /api/v1/utilities/resolve, public resolver tables, standard API-key auth, GET /api/v1/utilities/deprecated (M10 replacement). Preserve Shipped/In-Flight/Next-Up status blocks. Mark M1/M2/M6-original as SUPERSEDED with pointer to PR #233. Push as a single mono PR for Victor to see.