fix: force IPv4 in Caddy build (Docker lacks IPv6 during build)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/deploy/docker/Dockerfile.caddy

@@ -1,7 +1,10 @@
 # Caddy with Cloudflare DNS plugin — builds for any arch
 FROM caddy:2-builder AS builder
 
-RUN xcaddy build \
+# Force IPv4-only for Go module downloads (Docker build may lack IPv6)
+ENV GOFLAGS="-mod=mod"
+RUN echo 'precedence ::ffff:0:0/96 100' > /etc/gai.conf && \
+    xcaddy build \
     --with github.com/caddy-dns/cloudflare
 
 FROM caddy:2