Set up repo structure and implement base role

- Document architecture decisions in README (Ansible + Docker Compose + Traefik)
- Scaffold Ansible layout: inventory, site.yml, group_vars, 9 service roles
- Implement base role: package install, deploy user, SSH hardening,
  UFW firewall (22/80/443), fail2ban, unattended-upgrades
- Add reinstall runbook in docs/runbook.md
- Add ansible/requirements.yml for community.general and ansible.posix

ansible/roles/base/files/20auto-upgrades

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+APT::Periodic::Update-Package-Lists "1";
+APT::Periodic::Unattended-Upgrade "1";

ansible/roles/base/handlers/main.yml

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+---
+- name: Restart sshd
+  ansible.builtin.service:
+    name: ssh
+    state: restarted

ansible/roles/base/tasks/main.yml

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+---
+# --- Packages ---
+
+- name: Update apt cache
+  ansible.builtin.apt:
+    update_cache: true
+    cache_valid_time: 3600
+  tags: base
+
+- name: Upgrade all packages
+  ansible.builtin.apt:
+    upgrade: dist
+  tags: base
+
+- name: Install base packages
+  ansible.builtin.apt:
+    name:
+      - curl
+      - git
+      - vim
+      - htop
+      - ufw
+      - fail2ban
+      - unattended-upgrades
+      - apt-listchanges
+    state: present
+  tags: base
+
+# --- System ---
+
+- name: Set timezone
+  community.general.timezone:
+    name: "{{ timezone }}"
+  tags: base
+
+# --- Deploy user ---
+
+- name: Create deploy user
+  ansible.builtin.user:
+    name: "{{ deploy_user }}"
+    shell: /bin/bash
+    create_home: true
+    groups: sudo
+    append: true
+    state: present
+  tags: base
+
+- name: Add SSH authorized key for deploy user
+  ansible.posix.authorized_key:
+    user: "{{ deploy_user }}"
+    state: present
+    key: "{{ lookup('file', playbook_dir + '/../keys/notroot_cloud_ladkau_de.pub') }}"
+  tags: base
+
+- name: Allow deploy user passwordless sudo
+  ansible.builtin.copy:
+    dest: /etc/sudoers.d/{{ deploy_user }}
+    content: "{{ deploy_user }} ALL=(ALL) NOPASSWD:ALL\n"
+    mode: "0440"
+    validate: visudo -cf %s
+  tags: base
+
+# --- SSH hardening ---
+
+- name: Deploy hardened sshd_config
+  ansible.builtin.template:
+    src: sshd_config.j2
+    dest: /etc/ssh/sshd_config
+    owner: root
+    group: root
+    mode: "0600"
+    validate: sshd -t -f %s
+  notify: Restart sshd
+  tags: base
+
+# --- Firewall ---
+
+- name: Set UFW default incoming policy to deny
+  community.general.ufw:
+    direction: incoming
+    policy: deny
+  tags: base
+
+- name: Set UFW default outgoing policy to allow
+  community.general.ufw:
+    direction: outgoing
+    policy: allow
+  tags: base
+
+- name: Allow SSH (22/tcp)
+  community.general.ufw:
+    rule: allow
+    port: "22"
+    proto: tcp
+  tags: base
+
+- name: Allow HTTP (80/tcp)
+  community.general.ufw:
+    rule: allow
+    port: "80"
+    proto: tcp
+  tags: base
+
+- name: Allow HTTPS (443/tcp)
+  community.general.ufw:
+    rule: allow
+    port: "443"
+    proto: tcp
+  tags: base
+
+- name: Enable UFW
+  community.general.ufw:
+    state: enabled
+  tags: base
+
+# --- Automatic security updates ---
+
+- name: Enable unattended-upgrades
+  ansible.builtin.copy:
+    src: 20auto-upgrades
+    dest: /etc/apt/apt.conf.d/20auto-upgrades
+    owner: root
+    group: root
+    mode: "0644"
+  tags: base
+
+# --- Fail2ban ---
+
+- name: Enable and start fail2ban
+  ansible.builtin.service:
+    name: fail2ban
+    state: started
+    enabled: true
+  tags: base

ansible/roles/base/templates/sshd_config.j2

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+# Managed by Ansible — do not edit manually
+Port 22
+Protocol 2
+
+# Authentication
+PermitRootLogin no
+PasswordAuthentication no
+ChallengeResponseAuthentication no
+PubkeyAuthentication yes
+AuthorizedKeysFile .ssh/authorized_keys
+
+# Only allow the deploy user over SSH
+AllowUsers {{ deploy_user }}
+
+# Misc hardening
+X11Forwarding no
+PrintMotd no
+MaxAuthTries 3
+LoginGraceTime 30
+
+UsePAM yes
+AcceptEnv LANG LC_*
+Subsystem sftp /usr/lib/openssh/sftp-server

ansible/roles/docker/tasks/main.yml

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+---
+# TODO: implement docker role

ansible/roles/gitea/tasks/main.yml

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+---
+# TODO: implement gitea role

ansible/roles/k8s/tasks/main.yml

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+---
+# TODO: implement k8s role

ansible/roles/mail/tasks/main.yml

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+---
+# TODO: implement mail role

ansible/roles/nextcloud/tasks/main.yml

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+---
+# TODO: implement nextcloud role

ansible/roles/registry/tasks/main.yml

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+---
+# TODO: implement registry role

ansible/roles/sso/tasks/main.yml

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+---
+# TODO: implement sso role

ansible/roles/traefik/tasks/main.yml

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+---
+# TODO: implement traefik role