fix(db): enable test env cold-start migrations on empty database.

Use pgvector image with extensions-only init, seed legacy users before project/chat fixtures, and align test compose with goose-only schema bootstrap.

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

docker-compose.test.yml

@@ -9,7 +9,7 @@ name: agent-test
 
 services:
   system-db:
-    image: postgres:16-alpine
+    image: pgvector/pgvector:pg16
     container_name: shuimu-system-pg-test
     command: ["postgres", "-c", "shared_buffers=256MB", "-c", "max_connections=150"]
     environment:
@@ -20,7 +20,7 @@ services:
       - "127.0.0.1:${SYSTEM_DB_PUBLISH_PORT:-5434}:5432"
     volumes:
       - test-system-pgdata:/var/lib/postgresql/data
-      - ./deploy/postgres/system_init.sql:/docker-entrypoint-initdb.d/01-init.sql:ro
+      - ./deploy/postgres/extensions_init.sql:/docker-entrypoint-initdb.d/01-extensions.sql:ro
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${SYSTEM_DB_USER:-app} -d ${SYSTEM_DB_NAME:-agent_system_test}"]
       interval: 5s