CI: also build apps whose images don't exist yet

Handles first deploy — images aren't in the local registry yet,
so they must be built even if the diff doesn't touch app dirs.

.gitea/workflows/ci.yml

@@ -59,7 +59,8 @@ jobs:
             fi
 
             for app in blog market cart events federation account; do
-              if [ \"\$REBUILD_ALL\" = true ] || echo \"\$CHANGED\" | grep -q \"^\$app/\"; then
+              IMAGE_EXISTS=\$(docker image ls -q ${{ env.REGISTRY }}/\$app:latest 2>/dev/null)
+              if [ \"\$REBUILD_ALL\" = true ] || echo \"\$CHANGED\" | grep -q \"^\$app/\" || [ -z \"\$IMAGE_EXISTS\" ]; then
                 echo \"Building \$app...\"
                 docker build \
                   --build-arg CACHEBUST=\$(date +%s) \