feat(tf): hetzner_vm module (server + firewall + ssh key + cloud-init)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

terraform/modules/hetzner_vm/main.tf

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+# cloud-init: create the unprivileged `ansible` user with ubongo's key + sudo.
+# (Mirrors the proxmox_vm module's user_account; Hetzner has no structured field.)
+locals {
+  user_data = <<-EOT
+    #cloud-config
+    users:
+      - name: ansible
+        groups: [sudo]
+        sudo: "ALL=(ALL) NOPASSWD:ALL"
+        shell: /bin/bash
+        ssh_authorized_keys:
+          - ${var.ansible_ssh_pubkey}
+    package_update: true
+    packages:
+      - python3
+  EOT
+}
+
+resource "hcloud_ssh_key" "ansible" {
+  name       = "${var.name}-ansible"
+  public_key = var.ansible_ssh_pubkey
+}
+
+resource "hcloud_firewall" "this" {
+  name = "${var.name}-fw"
+
+  # SSH from the control node only. NetBird ports (UDP 3478, TCP 80/443) are added
+  # in M4 when the coordinator deploys (ADR-020); host nftables stays catalog-driven.
+  rule {
+    direction  = "in"
+    protocol   = "tcp"
+    port       = "22"
+    source_ips = var.ssh_admin_cidrs
+  }
+}
+
+resource "hcloud_server" "this" {
+  name         = var.name
+  server_type  = var.server_type
+  location     = var.location
+  image        = var.image
+  ssh_keys     = [hcloud_ssh_key.ansible.id]
+  user_data    = local.user_data
+  firewall_ids = [hcloud_firewall.this.id]
+  labels       = var.labels
+
+  public_net {
+    ipv4_enabled = true
+    ipv6_enabled = true
+  }
+}

terraform/modules/hetzner_vm/outputs.tf

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+output "ipv4_address" {
+  description = "Server public IPv4"
+  value       = hcloud_server.this.ipv4_address
+}
+
+output "name" {
+  description = "Server name"
+  value       = hcloud_server.this.name
+}

terraform/modules/hetzner_vm/variables.tf

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+variable "name" {
+  description = "Server name (and hostname)"
+  type        = string
+}
+
+variable "server_type" {
+  description = "Hetzner server type, e.g. cax11 (ARM)"
+  type        = string
+}
+
+variable "location" {
+  description = "Hetzner location, e.g. hel1"
+  type        = string
+}
+
+variable "image" {
+  description = "OS image slug, e.g. debian-13"
+  type        = string
+}
+
+variable "ansible_ssh_pubkey" {
+  description = "Public SSH key provisioned for the ansible user via cloud-init"
+  type        = string
+}
+
+variable "ssh_admin_cidrs" {
+  description = "Source CIDRs allowed to reach SSH (e.g. ubongo's address/32)"
+  type        = list(string)
+}
+
+variable "labels" {
+  description = "Hetzner resource labels (metadata only)"
+  type        = map(string)
+  default     = {}
+}