ci: route build+deploy through lux-build-linux-amd64 ARC pool

The evo native runner has filesystem corruption — last 3 runs failed
at actions/checkout step ("Can't find action.yml under
/home/z/.arcd/runner/_work/_actions/actions/checkout/v4").

lux-build-linux-amd64 ARC pool on lux-k8s is healthy (listener idle,
0 runners, max 10). Per LLM.md cross-org rule, luxfi/* workflows must
target lux-build pool — never hanzo-build.

.github/workflows/build-lux.yml

@@ -31,7 +31,7 @@ env:
 
 jobs:
   build:
-    runs-on: evo
+    runs-on: lux-build-linux-amd64
     permissions:
       contents: read
       packages: write
@@ -80,7 +80,7 @@ jobs:
   deploy:
     needs: build
     if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request'
-    runs-on: evo
+    runs-on: lux-build-linux-amd64
     permissions:
       contents: read
     steps: