fix deployment by adding postgres service to base compose

.env.example

@@ -6,7 +6,12 @@ NPM_VERSION=latest
 APP_PORT=3000
 
 # Better Auth / PostgreSQL
+# For app running outside Docker, localhost is typical.
+# In Docker Compose deployment, default internal host is: postgres
 DATABASE_URL=postgres://postgres:postgres@localhost:5432/fiscal_clone
+POSTGRES_DB=fiscal_clone
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
 BETTER_AUTH_SECRET=replace-with-a-long-random-secret
 BETTER_AUTH_BASE_URL=http://localhost:3000
 BETTER_AUTH_ADMIN_USER_IDS=