feat(notesnook): migrate self-hosted Notesnook to k3s

Adds apps/notesnook (namespace, config, mongo rs0 StatefulSet, minio,
identity/sync/sse/monograph deployments + Traefik/cert-manager ingresses)
and argocd/notesnook.yaml. Secret applied out-of-band (only .example committed).
Includes design spec + implementation plan under docs/superpowers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/notesnook/sync-service.yaml

@@ -0,0 +1,10 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: notesnook-sync
+  namespace: notesnook
+spec:
+  selector:
+    app: notesnook-sync
+  ports:
+    - { name: http, port: 5264, targetPort: 5264 }