feat(phase0): bootstrap External Secrets Operator and fix helmfile dual-ownership

Phase 0 groundwork for helmfile→ArgoCD migration:

1. Remove 3 bootstrap releases from helmfile (cert-manager, reloader, ingress-nginx)
   — already managed by terraform/bootstrap-releases.tf; eliminates dual-ownership

2. Bootstrap ESO (External Secrets Operator) as TF-managed release
   — required for all ExternalSecret resources in phases 1-3
   — added to bootstrap-releases.tf + helm-repositories.tf

3. Create ClusterSecretStore connecting ESO to Vault (K8s auth)
   — enables per-namespace/per-release secret injection
   — vault config documented in docs/PHASE0-ESO-VAULT-SETUP.md (manual setup)

4. Fix argocd-bootstrap.tf CA cert copy: use jq instead of sed for cleaner metadata handling

Changes:
- helmfile.yaml.gotmpl: remove cert-manager/reloader/ingress-nginx blocks
- terraform/bootstrap-releases.tf: add external-secrets release
- terraform/helm-repositories.tf: add external-secrets Helm repo
- k8s/external-secrets/clustersecretstore.yaml: ESO→Vault ClusterSecretStore
- k8s/argocd/apps/0-wave-0.yaml: stub wave 0 applications (schema fix, rewrite pending Phase 1)
- docs/PHASE0-ESO-VAULT-SETUP.md: manual ESO-Vault auth setup procedure

Next: Phase 1 will incrementally rewrite ArgoCD Applications + migrate helmfile releases.

Co-Authored-By: Claude Haiku 4.5 <[email protected]>

terraform/state.tf

@@ -1,4 +1,3 @@
-# S3 backend (MinIO remote state)
 terraform {
   backend "s3" {
     bucket                      = "terraform-state"