Adds binary mirroring to release-image.sh: cross-compiled binaries from
zddc/dist/ are now copied to website/releases/zddc-server-<os>-<arch>-<channel>
for every channel in the cascade, so https://zddc.varasys.io/releases/
serves binaries alongside the HTML tools. Channel pointers are mutable;
no immutable per-version files are written (the container registry
provides per-version pinning via image tags).
Plain `sh build.sh` does NOT mirror binaries — only `release-image.sh`
does, deliberately, to avoid 40MB git churn per dev iteration.
This commit also picks up the routine alpha-mirror refresh from the
v0.0.8-alpha.2 image cut.
