Implemented all service roles

- docker: install Docker Engine from official apt repo, configure log rotation,
  create shared traefik_public network
- traefik: reverse proxy with automatic Let's Encrypt TLS, dashboard on
  cloud.ladkau.de behind basic auth
- gitea: self-hosted Git with PostgreSQL, Git-over-SSH on port 2222
- sso: Keycloak with PostgreSQL for OIDC/OAuth2 single sign-on
- nextcloud: file storage with PostgreSQL, Redis, cron sidecar, CalDAV/CardDAV
  well-known redirects
- mail: Roundcube webmail client with PostgreSQL
- registry: Docker Registry v2 with htpasswd auth, no upload size limit
- k8s: placeholder nginx page

All secrets documented in vault.yml; runbook updated with per-service
first-run notes.

ansible/roles/mail/tasks/main.yml

@@ -1,2 +1,30 @@
 ---
-# TODO: implement mail role
+# Roundcube webmail client — connects to any external IMAP/SMTP server
+- name: Create Roundcube data directories
+  ansible.builtin.file:
+    path: "{{ item }}"
+    state: directory
+    owner: root
+    group: root
+    mode: "0750"
+  loop:
+    - "{{ mail_data_dir }}"
+    - "{{ mail_data_dir }}/db"
+  tags: mail
+
+- name: Deploy Docker Compose file
+  ansible.builtin.template:
+    src: docker-compose.yml.j2
+    dest: "{{ mail_data_dir }}/docker-compose.yml"
+    owner: root
+    group: root
+    mode: "0644"
+  notify: Restart mail
+  tags: mail
+
+- name: Start Roundcube
+  community.docker.docker_compose_v2:
+    project_src: "{{ mail_data_dir }}"
+    state: present
+    pull: missing
+  tags: mail