Function parseCompletionManifest

Returns {
    claims: {
        artifact_sha256s: string[];
        claim_id: string;
        provider: { id: string; version: string };
        result_schema_version: number;
        scenario: { id: string; version: number };
    }[];
    environment: {
        architecture: string;
        platform: string;
        runtime: string;
        runtime_version: string;
    };
    manifest_id: string;
    schema_version: 1;
    skill_digests: { sha256: string; skill_id: string }[];
    verifier: { id: string; version: string };
}