Follow the builder image to the build org

A package namespace does not travel with the repo and gets no redirect,
so the image had stayed in internal/ after the org reorganization. It
now lives under build/, next to this repo.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

builder.Dockerfile

@@ -9,8 +9,8 @@
 #
 # Build & push (the CI runner is linux/amd64):
 #   docker build --platform linux/amd64 -f builder.Dockerfile \
-#     -t git.teletypegames.org/internal/love-builder:latest .
-#   docker push git.teletypegames.org/internal/love-builder:latest
+#     -t git.teletypegames.org/build/love-builder:latest .
+#   docker push git.teletypegames.org/build/love-builder:latest
 
 FROM alpine:3.22