feat: migrate cluster baseline from Hetzner to Proxmox

Replace Hetzner infrastructure and cloud-provider assumptions with Proxmox
VM clones, kube-vip API HA, and NFS-backed storage. Update bootstrap,
Flux addons, CI workflows, and docs to target the new private Proxmox
baseline while preserving the existing Tailscale, Doppler, Flux, Rancher,
and B2 backup flows.

ansible/roles/k3s-server/tasks/main.yml

@@ -61,7 +61,7 @@
     --cluster-init
     --advertise-address={{ k3s_primary_ip }}
     --node-ip={{ k3s_node_ip }}
-    --flannel-iface=enp7s0
+    --flannel-iface={{ k3s_flannel_iface }}
     --tls-san={{ k3s_primary_ip }}
     --tls-san={{ k3s_primary_public_ip }}
     --tls-san={{ kube_api_endpoint }}
@@ -87,7 +87,7 @@
         --server https://{{ k3s_join_endpoint | default(k3s_primary_ip) }}:6443
         --advertise-address={{ k3s_node_ip }}
         --node-ip={{ k3s_node_ip }}
-        --flannel-iface=enp7s0
+        --flannel-iface={{ k3s_flannel_iface }}
         {% if k3s_disable_embedded_ccm | bool %}--disable-cloud-controller{% endif %}
         {% if k3s_disable_servicelb | bool %}--disable=servicelb{% endif %}
         {% if k3s_kubelet_cloud_provider_external | bool %}--kubelet-arg=cloud-provider=external{% endif %}