fix(e2e): make Polaris e2e CI self-sufficient with RBAC in workflow

Canonical fix for PRI-513: resolve Polaris e2e CI failures by applying
RBAC directly in the workflow rather than depending on pre-existing
Flux-managed RBAC that may not have converged.

Changes:
- .github/workflows/e2e.yaml: add workflow steps to apply both
  e2e-ci-runner-rbac.yaml (headlamp-dev namespace) and polaris-rbac.yaml
  (polaris namespace) before the pre-flight check, plus a pre-flight
  RBAC verification step
- deployment/e2e-ci-runner-rbac.yaml: add a Role + RoleBinding for the
  polaris namespace so the CI runner can apply polaris-rbac.yaml

This is the canonical form combining the best elements of stacking PRs:
- Self-sufficient workflow (no external RBAC dependency)
- RBAC pre-flight check for fast failure
- read-write permissions for polaris namespace (same as main stacks)

Supersedes: PRs #122, #124, #125

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/e2e.yaml

@@ -45,6 +45,26 @@ jobs:
       - name: Setup kubectl
         uses: azure/setup-kubectl@v4
 
+      - name: Apply RBAC for E2E pipeline
+        run: kubectl apply -f deployment/e2e-ci-runner-rbac.yaml
+
+      - name: Apply Polaris dashboard RBAC
+        run: kubectl apply -f deployment/polaris-rbac.yaml
+
+      - name: RBAC pre-flight check
+        run: |
+          echo "Checking RBAC resources..."
+          MISSING=0
+          kubectl get role polaris-dashboard-proxy-reader -n polaris -o name >/dev/null 2>&1 || MISSING=1
+          kubectl get rolebinding polaris-dashboard-proxy-reader -n polaris -o name >/dev/null 2>&1 || MISSING=1
+          kubectl auth can-i delete configmaps -n "$E2E_NAMESPACE" --quiet 2>/dev/null || MISSING=1
+          if [ "$MISSING" -eq 0 ]; then
+            echo "RBAC pre-flight check passed."
+          else
+            echo "::error::RBAC pre-flight check failed. Missing required permissions."
+            exit 1
+          fi
+
       - name: Install dependencies
         run: npm ci