add darwin support to install homebrew deps

roles/darwin/README.md

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+# Darwin (macOS)
+
+Baseline macOS hosts through Homebrew. No-op on non-Darwin targets.
+
+Configure in `inventory/host_vars/<host>/vars.yml`:
+
+```yaml
+darwin_homebrew_update: false   # update formula metadata before installing
+darwin_taps:
+  - anomalyco/tap
+darwin_formulae:
+  - jq
+  - ripgrep
+darwin_casks:
+  - iterm2
+```
+
+Casks install GUI apps; leave the list empty if you don't want them managed.
+Requires the `community.general` collection (`homebrew`, `homebrew_tap`,
+`homebrew_cask`). Must run as the Homebrew-owning user — never with `become`.

roles/darwin/defaults/main.yml

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+---
+# macOS baseline managed through Homebrew. No-op on non-Darwin hosts.
+darwin_homebrew_update: false
+darwin_taps: []
+darwin_formulae: []
+darwin_casks: []

roles/darwin/meta/main.yml

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+---
+galaxy_info:
+  author: Jokester <main@jokester.fr>
+  description: macOS baseline via Homebrew (taps, formulae, casks)
+  license: MIT
+  min_ansible_version: "2.15"
+  galaxy_tags:
+    - macos
+    - homebrew
+  platforms:
+    - name: MacOSX
+      versions:
+        - all
+dependencies: []

roles/darwin/tasks/main.yml

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+---
+- name: Assert the target is macOS
+  ansible.builtin.assert:
+    that:
+      - ansible_facts['os_family'] == 'Darwin'
+    fail_msg: "The darwin role only supports macOS (ansible_os_family == 'Darwin')."
+    success_msg: "macOS target validated"
+
+# Homebrew refuses to run as root: keep this role out of any become context.
+- name: Update Homebrew metadata
+  community.general.homebrew:
+    update_homebrew: true
+  when: darwin_homebrew_update | bool
+
+- name: Tap Homebrew repositories
+  community.general.homebrew_tap:
+    name: "{{ item }}"
+    state: present
+  loop: "{{ darwin_taps }}"
+
+- name: Install Homebrew formulae
+  community.general.homebrew:
+    name: "{{ darwin_formulae }}"
+    state: present
+  when: darwin_formulae | length > 0
+
+- name: Install Homebrew casks
+  community.general.homebrew_cask:
+    name: "{{ darwin_casks }}"
+    state: present
+  when: darwin_casks | length > 0