feat(global_defaults): add system.mirror to schema and normalization

roles/global_defaults/defaults/main.yml

@@ -82,6 +82,7 @@ system_defaults:
   timezone: "Europe/Vienna"
   locale: "en_US.UTF-8"
   keymap: "us"
+  mirror: ""
   packages: []
   disks: []
   users: []

roles/global_defaults/tasks/_normalize_system.yml

@@ -10,6 +10,10 @@
         if (system_raw.name | default('') | string | trim | length) > 0
         else inventory_hostname
       }}
+    _mirror_defaults:
+      debian: "https://deb.debian.org/debian/"
+      ubuntu: "http://mirror.ubuntu.com/ubuntu/"
+      ubuntu-lts: "http://mirror.ubuntu.com/ubuntu/"
   ansible.builtin.set_fact:
     system_cfg:
       # --- Identity & platform ---
@@ -67,6 +71,12 @@
       timezone: "{{ system_raw.timezone | string }}"
       locale: "{{ system_raw.locale | string }}"
       keymap: "{{ system_raw.keymap | string }}"
+      mirror: >-
+        {{
+          system_raw.mirror | string | trim
+          if (system_raw.mirror | default('') | string | trim | length) > 0
+          else _mirror_defaults[system_raw.os | default('') | string | lower] | default('')
+        }}
       path: "{{ system_raw.path | default('') | string }}"
       packages: >-
         {{