refactor(bootstrap,configuration,environment): add defaults/main.yml and extract hardcoded values

roles/configuration/defaults/main.yml

@@ -0,0 +1,7 @@
+---
+# Network configuration dispatch — maps OS name to the task file
+# that writes network config. Default (NetworkManager) applies to
+# all OSes not explicitly listed.
+configuration_network_task_map:
+  alpine: network_alpine.yml
+  void: network_void.yml

roles/configuration/tasks/network.yml

@@ -30,8 +30,4 @@
     fail_msg: Failed to detect any network interfaces.
 
 - name: Configure networking
-  vars:
-    configuration_network_task_map:
-      alpine: network_alpine.yml
-      void: network_void.yml
   ansible.builtin.include_tasks: "{{ configuration_network_task_map[os] | default('network_nm.yml') }}"