docs(docker): use pgvector image for Postgres compose

Plain postgres:17 cannot load the vector extension required for semantic
search (#830). Switch to pgvector/pgvector:pg17 and document the requirement.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: rudi193-cmd

docker-compose-postgres.yml

@@ -1,13 +1,16 @@
 # Docker Compose configuration for Basic Memory with PostgreSQL
-# Use this for local development and testing with Postgres backend
+# Use this for local development and testing with Postgres backend.
+#
+# The Postgres backend requires the pgvector extension (semantic search).
+# This image bundles pgvector; plain postgres:17 will not work for vector search.
 #
 # Usage:
 #   docker-compose -f docker-compose-postgres.yml up -d
 #   docker-compose -f docker-compose-postgres.yml down
 
 services:
   postgres:
-    image: postgres:17
+    image: pgvector/pgvector:pg17
     container_name: basic-memory-postgres
     environment:
       # Local development/test credentials - NOT for production

docs/semantic-search.md

@@ -263,6 +263,7 @@ The sqlite-vec extension is loaded per-connection. Vector tables are created laz
 ### Postgres (cloud)
 
 - **Vector storage**: [pgvector](https://github.com/pgvector/pgvector) with HNSW indexing
+- **Local Docker**: use `docker-compose-postgres.yml` (`pgvector/pgvector:pg17`). Plain `postgres:17` lacks the extension; run `CREATE EXTENSION IF NOT EXISTS vector;` on any external instance before first migration.
 - **Chunk metadata table**: Created via Alembic migration (`search_vector_chunks` with `BIGSERIAL` primary key)
 - **Embedding table**: `search_vector_embeddings` created at runtime (dimension-dependent, same pattern as SQLite)
 - **Index**: HNSW index on the embedding column for fast approximate nearest-neighbour queries

tests/README.md

@@ -66,7 +66,7 @@ docker-compose -f docker-compose-postgres.yml up -d
 ```
 
 This starts:
-- Postgres 17 on port **5433** (not 5432 to avoid conflicts)
+- Postgres 17 with **pgvector** (`pgvector/pgvector:pg17`) on port **5433** (not 5432 to avoid conflicts)
 - Test database: `basic_memory_test`
 - Credentials: `basic_memory_user` / `dev_password`
 
@@ -121,7 +121,7 @@ jobs:
     # Postgres service container
     services:
       postgres:
-        image: postgres:17
+        image: pgvector/pgvector:pg17
         env:
           POSTGRES_DB: basic_memory_test
           POSTGRES_USER: basic_memory_user