GHCR OCI runtime validation

Trap: TypeScript-casting successful GHCR JSON looks safe because registry responses are conceptually typed, but malformed HTTP 200 payloads can select or cache bogus nightlies. Fix: require a trimmed, non-empty token with no surrounding whitespace; require annotation records to be non-array objects; and validate OCI schema version 2, layers, consumed media fields, finite non-negative sizes, and sha256:<hex> digests. Malformed or mismatched metadata remains terminal.