fix: set DOCKER_API_VERSION=1.40 for watchtower compatibility with Docker 29

Watchtower's latest image defaults to API version 1.25; Docker 29 raised
its minimum supported client API to 1.40, causing watchtower to crash on
every start. Setting DOCKER_API_VERSION=1.40 via env var overrides the
default without requiring a newer watchtower image.

docker-compose.yml

@@ -613,6 +613,7 @@ services:
     environment:
       - WATCHTOWER_NOTIFICATION_SKIP_TITLE=true
       - WATCHTOWER_NOTIFICATION_URL=ntfy://ntfy.ginnoir.com/watchtower?title=WatchtowerUpdates
+      - DOCKER_API_VERSION=1.40
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock