update: switch Terraform to NixOS template workflow

- Point clone_template to nixos-template and trim cloud-init to Nix-safe hostname/DNS only
- Remove SSH/Tailscale cloud-init variables and workflow secret dependencies
- Add reusable NixOS template-base config with bootloader, Tailscale, fish, and utility packages

terraform/variables.tf

@@ -66,13 +66,3 @@ variable "llama_vm_count" {
   default     = 1
   description = "How many Llama VMs to create"
 }
-
-variable "TS_AUTHKEY" {
-  type        = string
-  description = "Tailscale auth key used in cloud-init"
-}
-
-variable "SSH_KEY_PUBLIC" {
-  type        = string
-  description = "My Public SSH key for ssh auth list"
-}