n8n: add InfisicalStaticSecret for n8n-secret (centralize N8N_ENCRYPTION_KEY)

Out-of-band Secret -> Infisical homelab/prod /n8n. Parallel-name target
n8n-secret-infisical (Owner), passthrough of the single key encryption-key
(n8n's irrecoverable credentials-encryption root, lifted byte-identical).
Old secret stays live until decommission. ArgoCD-managed -> git->sync.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

n8n/infisical-n8n-secret.yaml

@@ -0,0 +1,28 @@
+apiVersion: secrets.infisical.com/v1beta1
+kind: InfisicalStaticSecret
+metadata:
+  name: n8n-secret
+  namespace: n8n
+spec:
+  # Shared, read-only machine identity (no write grant, no PushSecret).
+  # Source is the /n8n folder, single key encryption-key = N8N_ENCRYPTION_KEY.
+  # This is n8n's IRRECOVERABLE credentials-encryption root: it decrypts every
+  # credential stored in database.sqlite. Lifted BYTE-IDENTICAL (sha8 1fdb7832,
+  # len 32) — never regenerated. Also persisted verbatim in ~/.n8n/config on the
+  # PVC and backed up in the user's password manager (4-way redundancy).
+  # secretKeyRef.key is already 'encryption-key' -> straight passthrough.
+  infisicalAuthRef:
+    name: infisical-auth
+    namespace: infisical-operator
+  sources:
+    - projectId: 17e98e9d-70f5-43d1-8382-7da818dfcdd0   # project "homelab"
+      environmentSlug: prod
+      secretPath: /n8n
+  syncOptions:
+    refreshInterval: 60s
+  targets:
+    - kind: Secret
+      name: n8n-secret-infisical    # parallel name — old secret stays live until 3c
+      namespace: n8n
+      creationPolicy: Owner
+      # key passthrough: synced Secret carries encryption-key verbatim