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/apps/gotify/ingress.yaml

@@ -0,0 +1,26 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: gotify
+  namespace: notifications
+  annotations:
+    nginx.ingress.kubernetes.io/proxy-read-timeout: "600"
+    nginx.ingress.kubernetes.io/proxy-send-timeout: "600"
+    # WebSocket support for Gotify client connections
+    nginx.ingress.kubernetes.io/proxy-http-version: "1.1"
+    nginx.ingress.kubernetes.io/configuration-snippet: |
+      proxy_set_header Upgrade $http_upgrade;
+      proxy_set_header Connection "upgrade";
+spec:
+  ingressClassName: nginx
+  rules:
+    - host: gotify.riotpiao.com
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: gotify
+                port:
+                  number: 80