Omit ingestion metadata from /search records

[afoote-mitre]

Summary

Fixes #177. /search returned the indexed _source unchanged, exposing the internal opensearch_ops object inside otherwise complete CVE Records. This contradicted the documented response and introduced an extra top-level property that is not part of the CVE Record schema.

Why These Changes Were Needed

Change	Primary files	Reason
Omit top-level ingestion metadata at the public response boundary	utils/searchResponseBuilder.js	Copies each returned record without opensearch_ops, including its ingestion timestamps and signatures. The shared builder covers both direct searches and semantic searches after full-record retrieval, without mutating the indexed source or introducing a restrictive field allowlist.
Cover removal and record preservation	utils/searchResponseBuilder.test.js, routes/search.integration.test.js, controllers/searchController.test.js	Exercises published and rejected states, preserves CNA/ADP and other fields, checks source immutability, and verifies direct and semantic response paths.
Clarify response documentation	README.md, routes/swagger.js, generated api-docs/openapi.json	Explicitly describes the omitted ingestion field and distinguishes this targeted cleanup from CVE JSON schema validation or record repair.