#803 Stage 4 epic: cross-run pgvector memory (#agentic)

Swap postgres:16-alpine -> pgvector/pgvector:pg16 (volume-compatible, demo-gated). Migration CREATE EXTENSION vector + highway.agent_memory(memory_id, tenant_id, namespace, content, embedding vector(768), metadata JSONB, created_at) + HNSW index. enterprise/tools/memory.py memory_save/memory_search reusing rag.py Ollama embedding; namespace via fixed kwargs from agent spec (memory_namespace col from Stage 3). Optional auto_recall spec flag (default off): top-k prepended in init_goal seed. rag_search catalog entry wrapping rag.py. Gates: golden demos + harness + memory_roundtrip + namespace_isolation.