Bug Fix

Fix PgSearchIndex not persisting vectors when using RAGConfig.withSearchIndex

When RAGConfig.withSearchIndex(pgSearchIndex) was called, only the searchIndex field was set - pgVectorConnectionString remained None. This caused RAG.createHybridSearcher() to create an in-memory store, resulting in vectors not being persisted to PostgreSQL.

Changes:

• Add pgConfig method to SearchIndex trait to optionally expose DB config
• Implement pgConfig in PgSearchIndex to return its configuration
• Modify RAGConfig.withSearchIndex to auto-configure pgVector settings when a PgSearchIndex is provided
• Add RAGWithSearchIndexBugSpec tests to validate the fix

Impact: Users can now use RAGConfig.withSearchIndex(pgSearchIndex) and have both permission-aware methods AND regular ingest/query methods use the same PostgreSQL database for vector storage.