Add hybrid search developer guide

[mauvo]

Summary

• Adds a dedicated Hybrid search page to the GenAI ecosystem Developer Guide.
• Moves the worked full-text + vector WRRF example out of the Vector Search page and links to the new page.
• Adds a lexical + semantic + structural hybrid search example using a second vector index for structural embeddings.
• Adds Neo4j 5.11-compatible setup/query tabs using vector index procedures alongside the current Cypher 25 SEARCH examples.

Validation

• npm run build (exits 0; existing unrelated Asciidoctor warnings remain in demo pages)
• npm run lint
• python3 tools/docs-meta/scripts/hybrid_search_validation.py static --candidate all from docs-meta
• Live validation during drafting against Neo4j 5.11 and current Neo4j images for the 2-way and 3-way WRRF templates