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/secrets.yaml

@@ -0,0 +1,48 @@
+# Gotify secrets — SOPS-encrypt before committing!
+# sops -e -i k8s/apps/gotify/secrets.yaml
+#
+# After Gotify starts:
+# 1. Login to gotify.riotpiao.com with admin creds below
+# 2. Create an Application (e.g., "forgejo") → copy the app token
+# 3. Create a Client → copy the client token
+# 4. Update gotify-tokens secret with the client token
+# 5. Configure Forgejo webhook (see README below)
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: gotify-admin
+  namespace: notifications
+type: Opaque
+stringData:
+  username: admin
+  password: CHANGE_ME_BEFORE_DEPLOY
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: gotify-tokens
+  namespace: notifications
+type: Opaque
+stringData:
+  # Create after first login:
+  # - App token: Gotify UI → Applications → Create → copy token
+  # - Client token: Gotify UI → Clients → Create → copy token
+  app-token: CHANGE_AFTER_FIRST_LOGIN
+  client-token: CHANGE_AFTER_FIRST_LOGIN
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: gotify-smtp
+  namespace: notifications
+type: Opaque
+stringData:
+  # SMTP config for email forwarding
+  # Gmail example (use App Password, not account password):
+  host: smtp.gmail.com
+  port: "587"
+  from: [email protected]
+  user: CHANGE_ME
+  password: CHANGE_ME
+  notify-email: [email protected]