feat(proxmox): Proxmox VM template + Terraform/OpenTofu VM creation

Manual, documented bare-metal Proxmox install + cloud-init template build
(deliberately not automated — a fragile one-time step). Terraform/OpenTofu
config creates rn-platform-01/rn-lab-host-01 from that template via the
bpg/proxmox provider, with configurable (not hardcoded) VM sizing.

Validated: tofu fmt, tofu init -backend=false (real provider download),
tofu validate -> Success. No paid state backend required (local state).

infra/terraform/terraform.tfvars.example

@@ -0,0 +1,10 @@
+proxmox_api_url      = "https://proxmox.example.internal:8006/api2/json"
+proxmox_api_token    = "terraform@pve!rootnode=00000000-0000-0000-0000-000000000000"
+proxmox_node         = "pve"
+vm_disk_datastore    = "local-zfs"
+ssh_public_key       = "ssh-ed25519 AAAA... rootnode-deploy"
+management_cidr      = "203.0.113.0/24"
+
+# Override sizing here once real load data exists — see docs/CAPACITY_PLANNING.md.
+# platform_vm  = { cores = 4,  memory = 16384, disk_gb = 100 }
+# lab_host_vm  = { cores = 24, memory = 98304, disk_gb = 500 }