feat(gotify): add push notification server + SMTP email relay

- Gotify server (ghcr.io/gotify/server:2.6.1) in notifications namespace
- SMTP emailer sidecar polls messages, forwards as email via msmtp
- Ingress at gotify.riotpiao.com with WebSocket support
- 1Gi Longhorn PVC for message persistence
- ArgoCD Application (wave 8, auto-sync)
- Secrets template for admin creds, SMTP config, tokens
- README with setup guide: tokens, Forgejo webhooks, SMTP providers

Enables PR created/merged email notifications from Forgejo.

k8s/argocd/apps/59-gotify.yaml

@@ -0,0 +1,32 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: gotify
+  namespace: argocd
+  labels:
+    app.kubernetes.io/name: gotify
+    app.kubernetes.io/component: notifications
+  annotations:
+    argocd.argoproj.io/sync-wave: "8"
+spec:
+  project: homelab
+  revisionHistoryLimit: 3
+  source:
+    repoURL: https://forgejo.riotpiao.com/rock/homelab.git
+    targetRevision: main
+    path: k8s/apps/gotify
+  destination:
+    server: https://kubernetes.default.svc
+    namespace: notifications
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=true
+    retry:
+      limit: 5
+      backoff:
+        duration: 5s
+        factor: 2
+        maxDuration: 3m