harbor: upstream v2.15 images are amd64-only, so the Harbor app cannot run on arm64 #4520

The Harbor app doesn't run on arm64. Every Harbor component crash-loops with exec format error, because the upstream images for v2.15.1 are amd64 only. That is the version the vendored chart pins. The same holds for every v2.15.x release and release candidate, up to v2.15.3-rc2.

Upstream added multi-arch builds on main in May 2026 (goharbor/harbor#22311). So far only the dev tag carries arm64, and no release has it yet. I expect the first multi-arch release to be 2.16.

On an arm64 test cluster Harbor starts once the component images point at dev, pinned by digest. That's fine for a test stand, not something to ship. Once upstream publishes a multi-arch release, the fix is to bump the vendored chart to it. Until then the Harbor app is amd64 only.

Related to #1961.