Add docker-compose.yml following stwaddle stack pattern

Joins web (nginx-proxy), apps-internal (database), and auth-public
(OIDC discovery without hairpinning) networks. External networks are
pre-created by the stwaddle infra compose; apps-db is defined here
so the budget service can be deployed standalone.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,40 @@
+services:
+  budget:
+    image: ${IMAGE_REGISTRY:-}budget:latest
+    environment:
+      - VIRTUAL_HOST=${BUDGET_VIRTUAL_HOST:-budget.stwaddle.com}
+      - LETSENCRYPT_HOST=${BUDGET_LETSENCRYPT_HOST:-budget.stwaddle.com}
+      - VIRTUAL_PORT=8080
+      - ASPNETCORE_ENVIRONMENT=${ASPNETCORE_ENVIRONMENT:-Production}
+      - ConnectionStrings__DefaultConnection=Host=apps-db;Port=5432;Database=${POSTGRES_DB:-budget};Username=${POSTGRES_USER:-budget};Password=${POSTGRES_PASSWORD}
+    depends_on:
+      - apps-db
+      - auth
+    networks:
+      - web
+      - apps-internal
+      - auth-public
+    restart: unless-stopped
+
+  apps-db:
+    image: postgres:16-alpine
+    environment:
+      - POSTGRES_DB=${POSTGRES_DB:-budget}
+      - POSTGRES_USER=${POSTGRES_USER:-budget}
+      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD}
+    volumes:
+      - apps-db-data:/var/lib/postgresql/data
+    networks:
+      - apps-internal
+    restart: unless-stopped
+
+networks:
+  web:
+    external: true
+  apps-internal:
+    external: true
+  auth-public:
+    external: true
+
+volumes:
+  apps-db-data: