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.

.gitignore

@@ -52,6 +52,10 @@ terraform/*.tfstate.*
 terraform/zitadel/*.tfstate
 terraform/zitadel/*.tfstate.*
 terraform/zitadel/*.tfvars
+terraform/edge/*.tfstate
+terraform/edge/*.tfstate.*
+terraform/edge/*.tfvars
+terraform/edge/terraform.tfvars.local
 terraform.tfvars.local
 skills-lock.json
 secrets-plaintext.yaml