fix nvidia quota: use custom quota (32 CPU) instead of Kyverno-generated (16 CPU)

The GPU operator needs ~19 CPU limits across 16 pods (NFD, device plugin,
driver, validators, exporters). The Kyverno auto-generated quota of 16 CPU
was insufficient, blocking NFD worker and GC pods from scheduling.

- Add custom-quota label to nvidia namespace to exempt from Kyverno generation
- Add explicit ResourceQuota with limits.cpu=32, limits.memory=48Gi
- Fix: nvidia namespace tier label was missing after CI re-apply, causing
  Kyverno to use fallback LimitRange instead of tier-2-gpu specific one

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

stacks/platform/modules/nvidia/main.tf

@@ -13,6 +13,23 @@ resource "kubernetes_namespace" "nvidia" {
     labels = {
       "istio-injection" : "disabled"
       tier                               = var.tier
+      "resource-governance/custom-quota" = "true"
+    }
+  }
+}
+
+resource "kubernetes_resource_quota" "nvidia_quota" {
+  metadata {
+    name      = "tier-quota"
+    namespace = kubernetes_namespace.nvidia.metadata[0].name
+  }
+  spec {
+    hard = {
+      "limits.cpu"      = "32"
+      "limits.memory"   = "48Gi"
+      "requests.cpu"    = "8"
+      "requests.memory" = "8Gi"
+      pods              = "40"
     }
   }
 }