ci: use on-prem runners for E2E tests (#10)

Switch E2E tests from GitHub-hosted runners to self-hosted k3s-animaniacs
runners which have network access to headlamp.animaniacs.farh.net.

Changes:
- runs-on: k3s-animaniacs (from ubuntu-latest)
- Re-enable E2E on push/PR events
- Uses ARC (Actions Runner Controller) self-hosted runners

Resolves DNS resolution failures (ERR_NAME_NOT_RESOLVED) by using
runners in the same network as the Headlamp test instance.

Runner config: kubernetes/base/arc-runners/helmrelease-arc-runner-set.yaml

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Happy <yesreply@happy.engineering>

.github/workflows/e2e.yaml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   e2e:
-    runs-on: ubuntu-latest
+    runs-on: k3s-animaniacs
     timeout-minutes: 15
 
     steps: