feat: add Kanboard project management service

- Add kanboard subdomain to domains.yml
- Create Docker Compose template with SQLite backend and plugin store enabled
- Add Ansible task for service deployment
- Configure Caddy reverse proxy routing
- Integrate with productivity services category

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

group_vars/all/domains.yml

@@ -32,6 +32,7 @@ subdomains:
   bytestash: "snippets.{{ primary_domain }}"  # ByteStash code snippets
   gotify: "gotify.{{ primary_domain }}"  # Gotify notifications
   gotify_assistant: "gotify-assistant.{{ primary_domain }}"  # iGotify iOS assistant
+  kanboard: "kanboard.{{ primary_domain }}"  # Kanboard project management
 
 # Email domains for notifications
 email_domains: