nix-cache02: add native nix forgejo runner instance

Add a second runner instance (actions-native) that executes jobs
directly on the host, giving workflows persistent nix store access
and automatic binary cache population via Harmonia.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

terraform/vault/variables.tf

@@ -116,3 +116,10 @@ variable "forgejo_runner_token" {
   sensitive   = true
 }
 
+variable "forgejo_native_runner_token" {
+  description = "Forgejo Actions runner token for native nix runner on nix-cache02"
+  type        = string
+  default     = "PLACEHOLDER"
+  sensitive   = true
+}
+