Fix startup: correct watermark HTML concatenation; allow DATABASE env var; compose persists DB under /data; minor header css retains single Exit button

docker-compose.yml

@@ -10,10 +10,10 @@ services:
       - SECRET_KEY=${SECRET_KEY:-prod-secret}
       - ADMIN_USERNAME=${ADMIN_USERNAME:-ruslan}
       - ADMIN_PASSWORD=${ADMIN_PASSWORD:-utOgbZ09ruslan}
+      - DATABASE=/data/app.db
     volumes:
-      - appdb:/app/app.db
+      - appdb:/data
     restart: unless-stopped
 
 volumes:
   appdb: {}
-