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/kanboard.yml

@@ -0,0 +1,18 @@
+---
+- name: Create kanboard directories
+  ansible.builtin.file:
+    path: "{{ item }}"
+    state: directory
+  loop:
+    - /opt/stacks/kanboard
+
+- name: Template kanboard compose file
+  ansible.builtin.template:
+    src: kanboard-compose.yml.j2
+    dest: /opt/stacks/kanboard/compose.yml
+
+- name: Deploy kanboard stack
+  community.docker.docker_compose_v2:
+    project_src: /opt/stacks/kanboard
+    files:
+      - compose.yml