Add transmission role for torrent-based ZIM downloads

- Add new transmission ansible role using homebrew + brew services
- Configure transmission to download to ~/transmission with localhost-only RPC
- Modify kiwix role to use transmission for downloading ZIM archives via BitTorrent
- Add role dependency so running --tags kiwix auto-runs transmission
- Keep fallback to direct HTTP download when kiwix_use_transmission: false
- Symlink completed downloads from transmission dir to kiwix-tools dir

This reduces load on kiwix.org servers and allows downloads to continue
in the background without blocking ansible runs.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ansible/roles/transmission/tasks/main.yml

@@ -0,0 +1,42 @@
+---
+- name: Install transmission-cli via homebrew
+  community.general.homebrew:
+    name: transmission-cli
+    state: present
+
+- name: Ensure transmission download directory exists
+  ansible.builtin.file:
+    path: "{{ transmission_download_dir }}"
+    state: directory
+    mode: '0755'
+
+- name: Ensure transmission incomplete directory exists
+  ansible.builtin.file:
+    path: "{{ transmission_incomplete_dir }}"
+    state: directory
+    mode: '0755'
+
+- name: Ensure transmission config directory exists
+  ansible.builtin.file:
+    path: "{{ transmission_config_dir }}"
+    state: directory
+    mode: '0755'
+
+- name: Stop transmission before config changes
+  ansible.builtin.command: brew services stop transmission-cli
+  register: brew_stop
+  changed_when: false
+  failed_when: false
+
+- name: Deploy transmission settings.json
+  ansible.builtin.template:
+    src: settings.json.j2
+    dest: "{{ transmission_config_dir }}/settings.json"
+    mode: '0644'
+  notify: restart transmission
+
+- name: Ensure transmission service is started
+  ansible.builtin.command: brew services start transmission-cli
+  register: brew_start
+  changed_when: "'Successfully started' in brew_start.stdout"
+  failed_when: false