Add Spinner, a Minecraft hostname-routing reverse proxy

Routes Java Edition connections by the hostname in the handshake, with
wildcard domains, backend failover, PROXY protocol v2, cached server-list
status from health probes, hot-reloaded config, and an admin page and
metrics endpoint. Includes CI, tagged releases and a container image.

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

Dockerfile

@@ -0,0 +1,20 @@
+# syntax=docker/dockerfile:1
+# Packages the binary deploy/build.sh already built (dist/bin/linux_<arch>/spinner),
+# so the image needs no Go toolchain and no emulation. Build it with:
+#   sh deploy/build.sh && docker buildx build .
+FROM --platform=$BUILDPLATFORM alpine:3.22 AS prep
+RUN mkdir /data && chown 65532:65532 /data
+
+FROM scratch
+ARG TARGETARCH
+LABEL org.opencontainers.image.title="Spinner" \
+      org.opencontainers.image.description="Minecraft hostname-routing reverse proxy" \
+      org.opencontainers.image.source="https://git.veillax.com/Veillax/Spinner" \
+      org.opencontainers.image.licenses="AGPL-3.0-only"
+COPY --from=prep --chown=65532:65532 /data /data
+COPY dist/bin/linux_${TARGETARCH}/spinner /spinner
+USER 65532:65532
+VOLUME ["/data"]
+EXPOSE 25565 8080
+ENTRYPOINT ["/spinner"]
+CMD ["-config", "/data/spinner.json"]