Fix 3 Code Review findings on FRE-4574

- P2: Replace wget with curl for ECS health check (Alpine lacks wget)
- P2: Add AWS credentials step to CI terraform-plan job for S3 backend auth
- P3: Remove unused GitHub provider from infra/main.tf

Co-Authored-By: Paperclip <noreply@paperclip.ing>

infra/variables.tf

@@ -114,3 +114,9 @@ variable "secrets" {
   type        = map(string)
   default     = {}
 }
+
+variable "domain_name" {
+  description = "Route53 hosted zone domain for ACM cert validation"
+  type        = string
+  default     = "shieldai.app"
+}