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/k8s/external-secrets/cluster-secret-store.yaml

@@ -0,0 +1,23 @@
+---
+# ClusterSecretStore — connects ESO to Vault using the root token Secret.
+# The vault-token Secret (name: vault-token, key: token) must be created
+# via kubectl as a one-time bootstrap step before this store can sync:
+#
+#   kubectl create secret generic vault-token \
+#     --namespace external-secrets \
+#     --from-literal=token=$(cat ~/Secrets/tokens/vault-root-token)
+apiVersion: external-secrets.io/v1beta1
+kind: ClusterSecretStore
+metadata:
+  name: vault
+spec:
+  provider:
+    vault:
+      server: "https://vault.neuralplatform.ai"
+      path: "secret"
+      version: "v2"
+      auth:
+        tokenSecretRef:
+          name: vault-token
+          namespace: external-secrets
+          key: token