feat: add paperclip-db PostgreSQL 17 service to AI compose stack

Adds paperclip-db service with postgres:17 image for Paperclip agent
orchestrator database backend. Uses POSTGRES_PASSWORD from env,
persistent volume at /mnt/HoardingCow_docker_data/Paperclip/db,
and healthcheck via pg_isready.

Requires .env: PAPERCLIP_DB_PASSWORD

ai/compose.yml

@@ -129,6 +129,22 @@ services:
       - "303"
       - "26"
 
+  paperclip-db:
+    image: postgres:17
+    container_name: paperclip-db
+    restart: always
+    environment:
+      - POSTGRES_PASSWORD=${PAPERCLIP_DB_PASSWORD}
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
+    volumes:
+      - /mnt/HoardingCow_docker_data/Paperclip/db:/var/lib/postgresql/data
+    networks:
+      - ai_backend
+
 networks:
   ai_net:
     external: true