feat: implement RAG indexing worker with vector database schema and document embedding support

db/migrations/0000013_rag_documents.up.sql

@@ -7,13 +7,14 @@ CREATE TABLE IF NOT EXISTS rag_chunks (
     project_id UUID REFERENCES projects(id) ON DELETE CASCADE,
     chunk_index INT NOT NULL,        
     content TEXT NOT NULL,            
-    embedding vector(3072),           
+    embedding vector(1536),           
     created_at TIMESTAMPTZ DEFAULT now(),
     updated_at TIMESTAMPTZ DEFAULT now()
 );
 
 CREATE INDEX idx_rag_chunks_source ON rag_chunks(source_type, source_id);
 CREATE INDEX idx_rag_chunks_project ON rag_chunks(project_id);
+CREATE INDEX idx_rag_chunks_embedding_hnsw ON rag_chunks USING hnsw (embedding vector_cosine_ops);
 
 CREATE TRIGGER trigger_rag_chunks_updated_at
 BEFORE UPDATE ON rag_chunks