fix(cilium): point cgroup.hostRoot at the host's real cgroup2 root

hostRoot was /run/cilium/cgroupv2 with autoMount disabled, but nothing
mounts cgroup2 there. The agent mounted one from inside its own private
cgroup namespace, so socket-LB attached to the agent's own cgroup and
host processes got no Service/LB translation. k3s-prod-1 (Gateway L2
lease holder + kube-vip VIP) therefore could not reach the Gateway VIP,
and its apiserver's OIDC authenticator has failed since 2026-09-12.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

infra/ansible/roles/cilium/templates/cilium-values.yaml.j2

@@ -51,11 +51,14 @@ hubble:
 l2announcements:
   enabled: true
 
-# k3s ships its own cgroup mount; point Cilium at it instead of auto-mounting.
+# Point Cilium at the host's real cgroup2 root (/sys/fs/cgroup, mounted by systemd) instead of
+# auto-mounting. NOT /run/cilium/cgroupv2: nothing mounts cgroup2 there, so the agent mounted its
+# OWN namespaced cgroup and socket-LB covered only itself — host processes (the apiserver) lost
+# Service/LB translation. [parity] platform/cilium/helmrelease.yaml explains (2026-10-03).
 cgroup:
   autoMount:
     enabled: false
-  hostRoot: /run/cilium/cgroupv2
+  hostRoot: /sys/fs/cgroup
 
 # Roll the cilium agent DaemonSet ONE node at a time. [parity] must match the
 # platform/cilium HelmRelease. The cilium 1.20.1 chart defaults this to 2, which on a