Add ntfy push notifications + mailrise SMTP bridge

- ntfy: self-hosted push notification service (port 8086)
- mailrise: SMTP-to-ntfy converter (port 8025)
- Configs in ./ntfy/server.yml and ./ntfy/mailrise.yml
- Token-based authentication for ntfy
- Updated docs and .gitignore

.gitignore

@@ -15,6 +15,8 @@
 !AGENTS.md
 !discord-agent/
 !discord-agent/**
+!ntfy/
+!ntfy/**
 
 # Never track actual secrets
 .env