Migrate k8s config from Terraform to Argo CD + ESO

Phase 1: Install External Secrets Operator via Argo CD app
- apps/external-secrets.yaml — ESO Helm chart install
- apps/external-secrets-config.yaml — ClusterSecretStore deployment
- k8s/external-secrets/cluster-secret-store.yaml — Vault backend using vault-token Secret

Phase 2: Create k8s manifests for all services
- k8s/neuron/ — PVC, ConfigMap, ExternalSecrets (neuron-secrets, cloudflared-secret), Ingress
- k8s/gitea/ — PVC, ConfigMap (custom CSS), ExternalSecret (gitea-db), Ingress
- k8s/github-runner/ — ExternalSecret (github-runner-secret)
- k8s/gitea-runner/ — ExternalSecret (gitea-runner-secret)
- k8s/monitoring/ — ExternalSecrets (grafana, slack), Alloy OTLP service+middleware, datasources ConfigMap, Ingress
- k8s/postgres/ — ExternalSecret (postgres-passwords)
- k8s/vault/ — ExternalSecret (vault-gcp-sa from Vault)
- k8s/adguard/ — PVCs, ConfigMap, Certificate, Ingress, ddclient Deployment+ExternalSecret
- k8s/ollama/ — PVC, Ingress
- k8s/headscale/ — PVC
- k8s/packages/ — PVCs, ConfigMap, Ingresses
- k8s/registry/ — PVC, Ingresses
- k8s/backup/ — CronJob, ExternalSecret (backup-credentials)

New Argo CD apps for Helm releases:
- apps/kube-prometheus-stack.yaml, loki.yaml, tempo.yaml, alloy.yaml
- apps/postgres.yaml, redis.yaml, vault.yaml

New Argo CD apps for k8s config paths:
- apps/neuron-config, gitea-config, ci-config, gitea-runner-config
- apps/monitoring-config, adguard-config, ollama-config, headscale-config
- apps/packages-config, registry-config, postgres-config, vault-config, backup

Phase 3: Strip Terraform to infrastructure-only
- All kubernetes_* and helm_release resources removed from service .tf files
- Each service .tf now contains only kubernetes_namespace (bootstrap dependency)
- variables.tf stripped to only cloudflare_api_key, cloudflare_email, gitea_api_token
- namespaces.tf gains external-secrets namespace
- ingress.tf, backup.tf, ddclient.tf emptied (resources in k8s/)
- cert-manager.tf, argocd.tf, traefik.tf unchanged (bootstrap)

servers/legion/headscale.tf

@@ -1,7 +1,6 @@
-# Headscale — self-hosted Tailscale control plane
-# Coordination endpoint: https://headscale.neuralplatform.ai (Cloudflare tunnel)
-# Clients: Tailscale app on Mac/iOS/Android, pointed at custom server
-# Subnet router: tailscaled on Legion host, advertises k3s + LAN CIDRs
+# Headscale — namespace only
+# PVC, Deployment, Service managed by Argo CD
+# See: apps/headscale.yaml, apps/headscale-config.yaml, k8s/headscale/
 
 resource "kubernetes_namespace" "headscale" {
   metadata {
@@ -12,22 +11,3 @@ resource "kubernetes_namespace" "headscale" {
     }
   }
 }
-
-resource "kubernetes_persistent_volume_claim" "headscale_data" {
-  metadata {
-    name      = "headscale-data"
-    namespace = kubernetes_namespace.headscale.metadata[0].name
-  }
-
-  # wait_until_bound = false because local-path only provisions on pod schedule
-  wait_until_bound = false
-
-  spec {
-    access_modes = ["ReadWriteOnce"]
-    resources {
-      requests = {
-        storage = "1Gi"
-      }
-    }
-  }
-}