[TASK] Migrate Search Layer

[fabrizzio-dotCMS]

Description

Complete vendor-neutral migration of the Search Layer. Content search is done; Site Search remains.

Layer: G5 – Search Layer | Dependency: G3 Mapping Layer completed (#34164)

Checklist

• Content search neutral API — SearchAPI, SearchAPIImpl, ESSearchAPIImpl, OSSearchAPIImpl extracted and phase-routed — PR feat(opensearch): extract vendor-neutral SearchAPI and phase-aware router #35609 ✅
• ESContentletAPIImpl — esSearch/esSearchRaw deprecated; neutral search/searchRaw delegates to SearchAPI — PR feat(opensearch): extract vendor-neutral SearchAPI and phase-aware router #35609 ✅
• ESSiteSearchAPI — create OS counterpart OSSiteSearchAPI; wire into phase-aware router
• SiteSearchAPI interface — remove Aggregation, ElasticsearchException ES types from public signatures — tracked in sub-task (see OpenSearch 3.x: Phase 1-2 - Client Development & Testing #33946)

Acceptance Criteria

• Site search routes correctly to ES (Phase 0/1) and OS (Phase 2/3)
• No org.elasticsearch.* in SiteSearchAPI public interface
• Existing site search integration tests pass against both providers

[github-actions]

PRs linked to this issue

• feat(opensearch): extract vendor-neutral SearchAPI and phase-aware router by @fabrizzio-dotCMS