upload-server/Dockerfile only packaged the goreleaser-built binary, so
the image could not be built from a checkout. It is now a multi-stage
build on Chainguard static, running as the nonroot user (uid 65532),
with a VARIANT=debug build arg that swaps in busybox for a shell.
The goreleaser packaging file moves unchanged to Dockerfile.release and
.goreleaser.yaml points at it, so the published netbirdio/upload image
stays as it was: distroless and root.
The bases are pinned by digest, since Chainguard publishes only :latest
for free. A Dependabot docker entry for /upload-server moves them
weekly, leaving the release base alone and holding golang to patch
updates.
