feat: built-in runbook template gallery

[HerbHall]

Summary

Ship curated runbook collections for common Docker workflows. Users can browse and import templates with one click.

Research Context

• Navi (16.8k stars): Community cheatsheet repos with navi repo add <url> -- proves demand for curated command collections
• Portainer: 500+ app templates via Lissy93/portainer-templates -- massive ecosystem
• Yacht: Decentralized template marketplace

Proposed Template Categories

1. Cleanup: System prune, dangling images, stopped containers, build cache
2. Monitoring: Container stats, resource usage, health checks, top processes
3. Debugging: Exec into container, inspect, logs with filtering, network diagnostics
4. Compose: Up/down/restart, rebuild single service, view service logs
5. Backup: Volume export, container commit, image save/load
6. Registry: Pull, push, tag, search, login

UX

• "Browse Templates" button in the main toolbar
• Gallery dialog with categories and preview
• "Import" button adds selected templates to the user's runbook collection
• Templates ship as bundled JSON, updateable via extension updates

References

• Navi community repos: https://github.com/denisidoro/navi#cheatsheet-repositories
• Portainer templates: https://github.com/Lissy93/portainer-templates