security: remove all REDACTED secrets from repo, add pre-commit guard

- Delete 26 secret manifests containing REDACTED placeholder values
  (15 cert-manager TLS + 11 app secrets across 8 namespaces)
- REDACTED is valid base64 that decodes to non-UTF-8 bytes — ArgoCD
  applying these manifests corrupts live secrets in the cluster
- Add .githooks/pre-commit that rejects any .yaml with REDACTED
- Add README.md documenting secret management policy and manual
  creation commands for each service
- n8n secret manifests already fixed in previous commits (618b1e8, db04fd2)

vaultwarden/secret-vaultwarden-secret.yaml

@@ -1,15 +0,0 @@
-apiVersion: v1
-data:
-  ADMIN_TOKEN: REDACTED
-  DOMAIN: REDACTED
-  SIGNUPS_ALLOWED: REDACTED
-kind: Secret
-metadata:
-  annotations:
-    kubectl.kubernetes.io/last-applied-configuration: '{"apiVersion":"v1","kind":"Secret","metadata":{"annotations":{},"name":"vaultwarden-secret","namespace":"vaultwarden"},"stringData":{"DOMAIN":"https://vaultwarden.chemavx.xyz","SIGNUPS_ALLOWED":"false"},"type":"Opaque"}
-
-      '
-  name: vaultwarden-secret
-  namespace: vaultwarden
-type: Opaque
-

vaultwarden/secret-vaultwarden-tls.yaml

@@ -1,21 +0,0 @@
-apiVersion: v1
-data:
-  tls.crt: REDACTED
-  tls.key: REDACTED
-kind: Secret
-metadata:
-  annotations:
-    cert-manager.io/alt-names: vaultwarden.chemavx.xyz
-    cert-manager.io/certificate-name: vaultwarden-tls
-    cert-manager.io/common-name: vaultwarden.chemavx.xyz
-    cert-manager.io/ip-sans: ''
-    cert-manager.io/issuer-group: cert-manager.io
-    cert-manager.io/issuer-kind: ClusterIssuer
-    cert-manager.io/issuer-name: letsencrypt-prod
-    cert-manager.io/uri-sans: ''
-  labels:
-    controller.cert-manager.io/fao: 'true'
-  name: vaultwarden-tls
-  namespace: vaultwarden
-type: kubernetes.io/tls
-