glean-migration-deep-dive

Migrate from Elasticsearch/Algolia: 1) Export all documents from source, 2) Transform to Glean document schema (id, title, url, body, permissions), 3) Create datasource with adddatasource, 4) Bulk index with bulkindexdocuments, 5) Validate search quality with test queries, 6) Switch search UI to use Glean Client API. Trigger: "glean migration deep dive", "migration-deep-dive".