fix(eurooffice): use ghcr.io image and cover missed integration spots

- pull document server from ghcr.io/euro-office/documentserver
- add selected-card styling for the EuroOffice office card
- teach update-helm.sh about the eurooffice deployment
- track Containers/eurooffice with dependabot
- align latest.yml env with containers.json
- mention EuroOffice in readme and QA checklist

AI-assistant: Claude Code 2.1.162 (Claude Opus 4.8)
Signed-off-by: Julius Knorr <jus@bitgrid.net>

.github/dependabot.yml

@@ -31,6 +31,7 @@ updates:
     - "/Containers/collabora"
     - "/Containers/docker-socket-proxy"
     - "/Containers/domaincheck"
+    - "/Containers/eurooffice"
     - "/Containers/fulltextsearch"
     - "/Containers/imaginary"
     - "/Containers/mastercontainer"