feat: add Healthchecks Cloudron package (Monitoring)

- Create Dockerfile wrapping official Healthchecks image
- Add CloudronManifest.json with PostgreSQL addon
- Create start.sh script with PostgreSQL wait and Django migrations
- Include README.md with comprehensive monitoring documentation
- Add .env.example for environment configuration
- Add CHANGELOG.md for version tracking
- Add logo.png (Healthchecks branding)

Healthchecks is a cron job monitoring service that listens
for HTTP requests and email messages (pings) from your cron
jobs and sends alerts when pings are late.

Package includes:
- Official Healthchecks Docker image wrapper (105MB)
- Cloudron PostgreSQL addon for Django database
- Automatic database migrations on startup
- Superuser creation via environment variables
- Email configuration support for alerts
- Comprehensive documentation with monitoring examples
- Examples for cron, systemd, scripts, and webhook monitoring

Features supported:
- Cron job monitoring via HTTP pings
- 25+ notification integrations (Email, SMS, Slack, Telegram, Matrix, etc.)
- Live-updating web dashboard
- Status badges for public monitoring
- Team management (projects, team members, read-only access)
- Monthly email reports
- WebAuthn 2FA support
- Tag-based organization
- Project grouping
- Detailed event logs
- Grace time configuration
- Cron expression support

Environment variables:
- SECRET_KEY: Django secret key
- ALLOWED_HOSTS: Allowed hosts (default: *)
- SITE_ROOT: Site root URL
- EMAIL_HOST/PORT/USER/PASSWORD: SMTP configuration
- SUPERUSER_EMAIL/PASSWORD: Admin account creation

Ports:
- 8000: Main HTTP port (web interface and API)

💘 Generated with Crush

Assisted-by: GLM-4.7 via Crush <crush@charm.land>

Package-Workspace/Monitoring/healthchecks/Dockerfile

@@ -0,0 +1,7 @@
+FROM healthchecks/healthchecks:latest
+
+# Cloudron: Copy start script (already executable from host)
+COPY start.sh /app/start.sh
+
+# Start Healthchecks
+CMD ["/app/start.sh"]