fix: increase Lambda timeout to 900s to cover CodeBuild poll window

Lambda was set to 300s but poll_codebuild_build loops for up to 12 min (720s).
Lambda would be killed by AWS before it could report back to CloudFormation.
900s gives a ~180s buffer beyond the poll window.

deploy/main.tf

@@ -43,7 +43,7 @@ module "eks_terragrunt_repo_generator" {
   lambda_config = {
     image_uri   = "${data.aws_caller_identity.current.account_id}.dkr.ecr.${data.aws_region.current.name}.amazonaws.com/eks-terragrunt-repo-generator/lambda:${var.image_tag}"
     memory_size = 512
-    timeout     = 300
+    timeout     = 900 # must exceed CodeBuild poll window (12 min = 720s)
 
     # VPC configuration (required for GitHub Enterprise access)
     vpc_config = var.enable_vpc ? {