ci: route goreleaser + release validate/create off ubuntu-latest to lux-build ARC

The v1.30.28 docker.yml run published node:v1.30.28 (sha-c36527c) fine on
the in-cluster lux-build ARC pool, but two sibling workflows red-X'd:

  - build.yml 'goreleaser' (runs on every push)
  - release.yml 'validate-version' (cascaded skips to every platform build)

Root cause: both pinned runs-on: ubuntu-latest. This org disables
GitHub-hosted runners (NO GITHUB BUILDERS) — ubuntu-latest jobs never get a
runner and fail at provisioning, not at compile. Source is sound:
GOWORK=off CGO_ENABLED=0 go build ./... is clean and the cross-layer
dexsettle_guard test passes (extras.DexSettleActivationTime ==
dex.DexSettleActivationTime == 1766704800 = 2025-12-25T23:20:00Z).

Route goreleaser, validate-version, and create-release to lux-build (the
org-scoped autoscalingrunnerset in lux-k8s that already builds the image).
GoReleaser cross-compiles every GOOS/GOARCH from one linux/amd64 host with
CGO disabled, so a single amd64 runner suffices.

(The per-platform binary reusables build-{ubuntu,linux,macos,win}-* still
pin classic [self-hosted,linux,amd64]/windows-2022 labels — a pre-existing
routing issue tracked separately; the node *image* path is unaffected.)

.github/workflows/build.yml

@@ -14,7 +14,12 @@ env:
 
 jobs:
   goreleaser:
-    runs-on: ubuntu-latest
+    # In-cluster ARC pool (lux-build autoscalingrunnerset in lux-k8s, org-scoped to
+    # github.com/luxfi, amd64). GitHub-hosted ubuntu-latest is disabled for this org
+    # (NO GITHUB BUILDERS) — that is why this job red-X'd while docker.yml (lux-build)
+    # published the image. GoReleaser cross-compiles all GOOS/GOARCH from one linux
+    # amd64 host with CGO_ENABLED=0, so a single amd64 runner is sufficient.
+    runs-on: lux-build
     steps:
       - name: Checkout
         uses: actions/checkout@v4

.github/workflows/release.yml

@@ -14,7 +14,10 @@ permissions:
 jobs:
   # Validate semantic version is < v2.0.0
   validate-version:
-    runs-on: ubuntu-latest
+    # lux-build ARC pool (in-cluster, lux-k8s, org-scoped to github.com/luxfi). The org
+    # disables GitHub-hosted runners (NO GITHUB BUILDERS); ubuntu-latest never gets a
+    # runner, which red-X'd this job and cascaded skips to every platform build below.
+    runs-on: lux-build
     outputs:
       version: ${{ steps.extract.outputs.version }}
       is_prerelease: ${{ steps.check.outputs.is_prerelease }}
@@ -94,7 +97,10 @@ jobs:
       - build-linux-binaries
       - build-macos
       - build-windows
-    runs-on: ubuntu-latest
+    # lux-build ARC pool (in-cluster, lux-k8s, org-scoped to github.com/luxfi). This job
+    # only downloads artifacts + cuts the GitHub Release — no compile — but ubuntu-latest
+    # is disabled for the org (NO GITHUB BUILDERS), so it must run on a self-hosted pool.
+    runs-on: lux-build
     steps:
       - name: Checkout code
         uses: actions/checkout@v4