Remove APP_VERSION from docker-compose — version is baked into image by CI

Setting APP_VERSION in docker-compose with a :-unknown fallback would override
the version baked into the image at build time. The CI already embeds it via
--build-arg APP_VERSION=1.0.<commit-count>, so compose should stay silent.

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

docker-compose/docker-compose.yml

@@ -263,7 +263,6 @@ services:
       - ASPNETCORE_URLS=${ASPNETCORE_URLS:-http://+:8080}
       - APP_ENVIRONMENT_NAME=${APP_ENVIRONMENT_NAME:-myai.staging}
 
-      - APP_VERSION=${APP_VERSION:-unknown}
       - Site__Mode=${Site__Mode:-Normal}
     networks:
       - myai-network