Merge branch 'feat/footer-share-ci' into dev

CI keeps the 'test once per code state' plan but records commit and
git tree as image labels instead of extra :sha-/:tree- tags, so the
registry only holds dev, latest, vX.Y.Z and stable; the plan test now
asserts the expected decisions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docker-compose.yml

@@ -42,6 +42,9 @@ services:
       - LEGAL_PRIVACY_CONTENT=${LEGAL_PRIVACY_CONTENT:-}
       - LEGAL_IMPRINT_CONTENT_FILE=${LEGAL_IMPRINT_CONTENT_FILE:-}
       - LEGAL_PRIVACY_CONTENT_FILE=${LEGAL_PRIVACY_CONTENT_FILE:-}
+      # Eigener Link im Footer (nur https://)
+      # - LEGAL_CUSTOM_LINK_LABEL=${LEGAL_CUSTOM_LINK_LABEL:-}
+      # - LEGAL_CUSTOM_LINK_URL=${LEGAL_CUSTOM_LINK_URL:-}
       # Bilder und Audio in Notizen
       - MEDIA_MAX_IMAGE_MB=${MEDIA_MAX_IMAGE_MB:-15}
       - MEDIA_MAX_AUDIO_MB=${MEDIA_MAX_AUDIO_MB:-50}