fix(gotify): CNPG Postgres backend, SOPS-encrypt secrets

- Replace SQLite + PVC with CNPG Postgres cluster (2 replicas, longhorn-cnpg)
- Connection string built at runtime via shell wrapper (env var interpolation)
- Remove gotify-data PVC (DB handles persistence)
- Encrypt secrets.yaml with SOPS
- Add db.yaml: gotify-db cluster in notifications namespace

k8s/apps/gotify/db.yaml

@@ -0,0 +1,35 @@
+# CNPG Postgres for Gotify. Lightweight — 2 instances, 2Gi storage.
+# CNPG generates secret `gotify-db-app` + service `gotify-db-rw` in ns notifications.
+apiVersion: postgresql.cnpg.io/v1
+kind: Cluster
+metadata:
+  name: gotify-db
+  namespace: notifications
+  annotations:
+    argocd.argoproj.io/sync-options: SkipDryRunOnMissingResource=true
+spec:
+  instances: 2
+  imageName: ghcr.io/cloudnative-pg/postgresql:16.2
+  bootstrap:
+    initdb:
+      database: gotify
+      owner: app
+      encoding: UTF8
+      localeCollate: C
+      localeCType: C
+  enableSuperuserAccess: false
+  resources:
+    requests: { memory: "256Mi", cpu: "100m" }
+    limits: { memory: "512Mi", cpu: "500m" }
+  storage:
+    size: 2Gi
+    storageClass: longhorn-cnpg
+  monitoring:
+    enablePodMonitor: true
+  affinity:
+    podAntiAffinityType: preferred
+    topologyKey: kubernetes.io/hostname
+    tolerations:
+      - key: node-role.kubernetes.io/control-plane
+        operator: Exists
+        effect: NoSchedule