ci: switch E2E workflow to ubuntu-latest runner

The k3s-animaniacs self-hosted runner is not available. Use GitHub-hosted
ubuntu-latest runner instead to enable automated E2E testing.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

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: k3s-animaniacs
+    runs-on: ubuntu-latest
     timeout-minutes: 15
 
     steps: