refactor(vars): remove legacy variable inputs

- Require hypervisor as dict input and use hypervisor_cfg/hypervisor_type internally

- Remove vm_* and hypervisor_* compatibility aliases

- Update roles and docs to use system/hypervisor dictionaries only

roles/global_defaults/defaults/main.yml

@@ -1,5 +1,7 @@
 ---
-hypervisor: "none"
+# User input. Normalized into hypervisor_cfg + hypervisor_type.
+hypervisor:
+  type: "none"
 hypervisor_defaults:
   type: "none"
   url: ""