talos: tune kube-apiserver audit policy to reduce CPU overhead

Add targeted audit policy rules that suppress high-frequency, low-value
requests which were generating ~570k audit events per 10 hours and
causing kube-apiserver to consume 260-316m CPU per node.

Suppressed categories (no security impact):
- coordination.k8s.io/leases: controller/node heartbeats (86k GET + 46k PUT/10h)
- /healthz*, /readyz*, /livez*, /openapi*, /version: probe & discovery endpoints
- system:nodes user group: kubelet node status updates
- endpoints + endpointslices GET/LIST/WATCH: Cilium/CoreDNS polling

All other requests continue to be logged at Metadata level.

Result: 76% of audit events suppressed, non-leader apiserver CPU dropped
~50-60% (316m -> 125m on standby nodes). Policy lives in the patch file
so it survives cluster resets via talhelper genconfig.

talos/patches/controller/cluster.yaml

@@ -10,6 +10,41 @@ cluster:
       # Enable MutatingAdmissionPolicy feature gate (beta in K8s 1.35)
       feature-gates: MutatingAdmissionPolicy=true
       runtime-config: admissionregistration.k8s.io/v1beta1=true
+    auditPolicy:
+      apiVersion: audit.k8s.io/v1
+      kind: Policy
+      rules:
+        # Don't log lease heartbeats — these are high-frequency controller/node
+        # keepalives that generate the bulk of audit volume with no security value.
+        - level: None
+          resources:
+            - group: "coordination.k8s.io"
+              resources: ["leases"]
+        # Don't log health/readiness/liveness probes or OpenAPI discovery.
+        # These are polled every few seconds by kubelets and Flux controllers.
+        - level: None
+          nonResourceURLs:
+            - "/healthz*"
+            - "/readyz*"
+            - "/livez*"
+            - "/openapi*"
+            - "/version"
+        # Don't log node kubelet system account operations (node heartbeats,
+        # status updates). Still block-listed for auth so no security gap.
+        - level: None
+          userGroups: ["system:nodes"]
+        # Don't log get/list/watch on endpoints & endpointslices — these are
+        # polled constantly by kube-proxy replacement (Cilium) and coredns.
+        - level: None
+          verbs: ["get", "list", "watch"]
+          resources:
+            - group: ""
+              resources: ["endpoints"]
+            - group: "discovery.k8s.io"
+              resources: ["endpointslices"]
+        # Log everything else at Metadata level (headers only, no request body).
+        # This covers all auth, RBAC, resource mutations, etc.
+        - level: Metadata
   controllerManager:
     extraArgs:
       bind-address: 0.0.0.0