Execute raw search query (POST)

Executes a raw JSON search query and returns the unprocessed search response in a portlet context. The request body accepts an Elasticsearch/OpenSearch JSON query. Unlike the /search endpoint, results are returned directly from the search engine without additional contentlet processing. The query is routed through the phase-aware search API, so it targets whichever engine the active OpenSearch migration phase selects (Elasticsearch in phases 0-1, OpenSearch in phases 2-3). The response preserves the legacy Elasticsearch-wire shape (took, hits.total, hits.hits[]._id/._index/._score/._source, aggregations, suggest) for backward compatibility, regardless of the engine that served the query.