[ci skip] Fix dashy OOMKilled and healthcheck DNS false-failure

- Add explicit resource limits to dashy (2Gi memory) to prevent OOMKilled
  during webpack build on startup
- Rewrite DNS healthcheck to test from inside the Technitium pod via
  kubectl exec, since MetalLB virtual IPs aren't reachable from outside
  the L2 network
- Deleted orphaned kured/tls-secret (expired Oct 2025, module disabled,
  not mounted by kured DaemonSet)

modules/kubernetes/dashy/main.tf

@@ -66,6 +66,16 @@ resource "kubernetes_deployment" "dashy" {
           image = "lissy93/dashy:latest"
           name  = "dashy"
 
+          resources {
+            requests = {
+              cpu    = "50m"
+              memory = "256Mi"
+            }
+            limits = {
+              cpu    = "1"
+              memory = "2Gi"
+            }
+          }
           port {
             container_port = 8080
           }