refactor: remove terraform entirely, migrate to pure GitOps (ArgoCD)

Delete entire terraform/ directory.

Architecture: Terraform + ArgoCD → ArgoCD only
- Single tool: ArgoCD manages all infrastructure and applications
- Source of truth: git only (k8s/ directory)
- Continuous reconciliation: no manual apply needed
- Simpler state: no tfstate backend, no state files

Next: Migrate all Terraform resources to k8s/ YAML manifests
and ArgoCD Applications (namespaces, storage classes, Helm releases,
RBAC, network policies, Authentik config).

terraform/main.tf

@@ -1,7 +0,0 @@
-locals {
-  cluster_domain = var.cluster_domain
-}
-
-# Helm repositories will be created in helm-repositories.tf
-# Namespaces will be created in bootstrap/namespaces.tf
-# Helm releases will be created in helm-releases/*.tf