feat(edge): Terraform for the China-facing relay and Cloudflare DNS

Adds terraform/edge, a root module with two providers:

- Cloudflare 5.28.1: CNAMEs to the existing tunnel, plus an opt-in resource that
  can take the tunnel ingress list over when manage_tunnel_config is true. It is
  off by default because that resource REPLACES the whole list, and the tunnel is
  remotely managed from the dashboard today.
- Tencent Cloud 1.83.38: VPC, subnet, security group with three rules, key pair,
  one CVM relay with cloud-init (WireGuard listener, forwarding sysctls, Caddy),
  and DNSPod A records for the .cn hostnames.

The design keeps the homelab inbound-free: the relay terminates TLS in China and
forwards over a WireGuard tunnel the cluster dials outbound. Cloudflare keeps
serving every existing hostname untouched.

Verified: terraform init succeeds for both providers, fmt clean, validate
reports 0 errors, and plan resolves to 10 creates with placeholder variables.
Provider-side name validation caught a real bug during that run: key pair and
security group names allow only letters, digits and underscore, so the derived
names use underscores.

Not applied. Credentials come from CLOUDFLARE_API_TOKEN,
TENCENTCLOUD_SECRET_ID and TENCENTCLOUD_SECRET_KEY; the WireGuard private key is
TF_VAR only. State is local and git-ignored like terraform/zitadel.

Blocked on facts this module cannot invent: the real .cn domain, whether it has
an ICP filing, the CVM image ID, the operator CIDR, and the homelab WireGuard
public key.

terraform/edge/variables.tf

@@ -0,0 +1,136 @@
+variable "cloudflare_api_token" {
+  description = "Cloudflare API token with Zone:DNS:Edit and, for tunnel config, Account:Cloudflare Tunnel:Edit."
+  type        = string
+  sensitive   = true
+  default     = null
+}
+
+variable "cloudflare_zone_id" {
+  description = "Zone ID of the existing public zone (riotpiao.com)."
+  type        = string
+}
+
+variable "cloudflare_account_id" {
+  description = "Account ID. Required only when manage_tunnel_config is true."
+  type        = string
+  default     = null
+}
+
+variable "tunnel_id" {
+  description = "UUID of the cloudflared tunnel that the DNS records point at."
+  type        = string
+}
+
+# The dashboard remains the source of truth for the remotely-managed tunnel
+# today. Setting this true hands that config to Terraform, which then rewrites
+# the whole ingress list: every hostname not listed in tunnel_ingress is
+# removed from the tunnel. Import first and read the plan before applying.
+variable "manage_tunnel_config" {
+  description = "Take ownership of the remotely-managed tunnel configuration."
+  type        = bool
+  default     = false
+}
+
+variable "tunnel_ingress" {
+  description = "hostname => origin service, used only when manage_tunnel_config is true."
+  type        = map(string)
+  default     = {}
+}
+
+# ── DNS records managed in the Cloudflare zone ───────────────────────────────
+# These names already exist, created by hand in the dashboard. Adopt them with
+# `terraform import` before the first apply, or Terraform will try to create a
+# second record with the same name and Cloudflare will reject it.
+variable "cloudflare_tunnel_hostnames" {
+  description = "Hostnames in the Cloudflare zone that must CNAME to the tunnel."
+  type        = list(string)
+  default     = []
+}
+
+# ── China edge ───────────────────────────────────────────────────────────────
+variable "china_domain" {
+  description = "The .cn domain served from Tencent Cloud, without a trailing dot."
+  type        = string
+}
+
+variable "china_hostnames" {
+  description = "Subdomains of china_domain that point at the Tencent relay."
+  type        = list(string)
+  default     = ["paperless", "img"]
+}
+
+variable "tencent_secret_id" {
+  description = "Tencent Cloud SecretId. Prefer TENCENTCLOUD_SECRET_ID in the environment."
+  type        = string
+  sensitive   = true
+  default     = null
+}
+
+variable "tencent_secret_key" {
+  description = "Tencent Cloud SecretKey. Prefer TENCENTCLOUD_SECRET_KEY in the environment."
+  type        = string
+  sensitive   = true
+  default     = null
+}
+
+variable "tencent_region" {
+  description = "Tencent Cloud region for the relay. Mainland regions need an ICP filing for the domain."
+  type        = string
+  default     = "ap-guangzhou"
+}
+
+variable "tencent_availability_zone" {
+  description = "Availability zone inside tencent_region."
+  type        = string
+  default     = "ap-guangzhou-6"
+}
+
+variable "relay_instance_type" {
+  description = "CVM spec for the relay. A relay only terminates TLS and forwards bytes."
+  type        = string
+  default     = "S5.SMALL2"
+}
+
+variable "relay_image_id" {
+  description = "CVM image ID. Find one with: tencentcloud images --image-name 'Ubuntu 24.04' (or the console)."
+  type        = string
+}
+
+variable "relay_ssh_public_key" {
+  description = "Public key injected into the relay for break-glass SSH. Never the private key."
+  type        = string
+}
+
+variable "relay_admin_cidr" {
+  description = "CIDR allowed to reach SSH on the relay. Keep it to the operator, not 0.0.0.0/0."
+  type        = string
+}
+
+variable "wireguard_port" {
+  description = "UDP port of the WireGuard listener on the relay."
+  type        = number
+  default     = 51820
+}
+
+variable "wireguard_relay_private_key" {
+  description = "WireGuard private key of the relay side. Generate with `wg genkey`; pass via TF_VAR_wireguard_relay_private_key."
+  type        = string
+  sensitive   = true
+}
+
+variable "wireguard_homelab_public_key" {
+  description = "WireGuard public key of the homelab peer that dials the relay."
+  type        = string
+}
+
+variable "wireguard_relay_address" {
+  description = "Tunnel address of the relay side."
+  type        = string
+  default     = "10.88.0.1/24"
+}
+
+variable "wireguard_homelab_address" {
+  description = "Tunnel address of the homelab side."
+  type        = string
+  default     = "10.88.0.2/24"
+}