fix: use headlamp-plugins-e2e namespace for E2E tests, revert workflow

headlamp-dev is Flux-managed (kustomization/headlamp-dev reconciles), causing
E2E deployment conflicts and test failures. Use a dedicated headlamp-plugins-e2e
namespace instead. Reverted .github/workflows/e2e.yaml — Hugh owns CI/CD; will
file a child issue to update the workflow namespace.

.github/workflows/e2e.yaml

@@ -11,7 +11,7 @@ permissions:
   contents: read
 
 # Only one E2E run at a time: the shared E2E_RELEASE (headlamp-e2e) in
-# headlamp-dev cannot be shared across concurrent runs.
+# privilegedescalation-dev cannot be shared across concurrent runs.
 # cancel-in-progress: false (queue, don't cancel) — cancelling in-flight
 # runs may skip the if: always() teardown, leaving dangling cluster resources.
 concurrency:
@@ -19,7 +19,7 @@ concurrency:
   cancel-in-progress: false
 
 env:
-  E2E_NAMESPACE: headlamp-dev
+  E2E_NAMESPACE: privilegedescalation-dev
   E2E_RELEASE: headlamp-e2e
   # Pin to a known-good Headlamp version. Using :latest is risky because
   # the tag can change between CI runs, causing flaky failures when a newer