refactor(bootstrap,configuration): add per-role _normalize.yml for platform resolution

roles/configuration/tasks/_normalize.yml

@@ -0,0 +1,16 @@
+---
+# Resolve platform-specific configuration for the target OS family.
+# Sets _configuration_platform from configuration_platform_config[os_family].
+- name: Resolve platform-specific configuration
+  ansible.builtin.assert:
+    that:
+      - os_family is defined
+      - os_family in configuration_platform_config
+    fail_msg: >-
+      Unsupported os_family '{{ os_family | default("undefined") }}'.
+      Extend configuration_platform_config in vars/main.yml.
+    quiet: true
+
+- name: Set platform configuration
+  ansible.builtin.set_fact:
+    _configuration_platform: "{{ configuration_platform_config[os_family] }}"