🐛 Retry GitHub API calls on rate-limit 403s during build 🐛

Parallel multi-platform builds (amd64 + arm64) fire ~14 unauthenticated
GitHub API calls concurrently — well over the 60 req/hr limit — causing
05-custom.sh to fail with a 403 on dominikh/go-tools (staticcheck).
Fix: _gh_latest now retries up to 3 times with a 60-second delay on
failure before giving up. A GITHUB_TOKEN build arg is also wired through
to the build stage ENV so callers can pass --build-arg GITHUB_TOKEN=$(gh
auth token) to raise the limit to 5000 req/hr and avoid the delay.
- Dockerfile: add ARG GITHUB_TOKEN="" and ENV GITHUB_TOKEN in build stage
- rootfs/root/docker/setup/05-custom.sh: retry loop (3 attempts, 60s backoff) in _gh_latest

Dockerfile
rootfs/root/docker/setup/05-custom.sh

Dockerfile

@@ -52,6 +52,9 @@ FROM ${PULL_URL}:${DISTRO_VERSION} AS build
 ARG TZ
 ARG USER
 ARG LICENSE
+# Optional: pass --build-arg GITHUB_TOKEN=$(gh auth token) to raise the API rate
+# limit from 60 to 5000 req/hr — avoids 403s in parallel multi-platform builds.
+ARG GITHUB_TOKEN=""
 ARG TIMEZONE
 ARG LANGUAGE
 ARG IMAGE_NAME
@@ -91,6 +94,7 @@ ENV GOTOOLCHAIN="auto"
 ENV GOFLAGS="-buildvcs=false"
 ENV GOTELEMETRY="off"
 ENV GOPROXY="https://proxy.golang.org,direct"
+ENV GITHUB_TOKEN="${GITHUB_TOKEN}"
 
 USER ${USER}
 WORKDIR /root