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>

roles/docker/tasks/productivity/main.yml

@@ -31,4 +31,8 @@
 
 - name: Install obsidian-livesync
   import_tasks: obsidian-livesync.yml
-  tags: obsidian-livesync
+  tags: obsidian-livesync
+
+- name: Install kanboard
+  import_tasks: kanboard.yml
+  tags: kanboard