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

roles/bootstrap/tasks/_normalize.yml

@@ -0,0 +1,24 @@
+---
+# Resolve the OS-specific variable namespace and task file for the bootstrap role.
+- name: Validate OS is supported for bootstrap
+  ansible.builtin.assert:
+    that:
+      - os is defined
+      - os in bootstrap_os_task_map
+    fail_msg: >-
+      Unsupported OS '{{ os | default("undefined") }}' for bootstrap.
+      Supported: {{ bootstrap_os_task_map | dict2items | map(attribute='key') | join(', ') }}
+    quiet: true
+  vars:
+    bootstrap_os_task_map:
+      almalinux: _dnf_family.yml
+      alpine: alpine.yml
+      archlinux: archlinux.yml
+      debian: debian.yml
+      fedora: _dnf_family.yml
+      opensuse: opensuse.yml
+      rocky: _dnf_family.yml
+      rhel: rhel.yml
+      ubuntu: ubuntu.yml
+      ubuntu-lts: ubuntu.yml
+      void: void.yml