refactor(global_defaults): data-driven hypervisor validation and shared constants

roles/global_defaults/defaults/main.yml

@@ -112,6 +112,42 @@ system_defaults:
     chroot:
       tool: "arch-chroot" # arch-chroot|chroot|systemd-nspawn
 
+# Per-hypervisor required fields — drives data-driven validation.
+# All virtual types additionally require network bridge or interfaces.
+hypervisor_required_fields:
+  proxmox:
+    hypervisor: [url, username, password, host, storage]
+    system: [id]
+  vmware:
+    hypervisor: [url, username, password, datacenter, cluster, storage]
+    system: []
+  xen:
+    hypervisor: []
+    system: []
+  libvirt:
+    hypervisor: []
+    system: []
+
+# Hypervisor-to-disk device prefix mapping for virtual machines.
+# Physical installs must set system.disks[].device explicitly.
+hypervisor_disk_device_map:
+  libvirt: "/dev/vd"
+  xen: "/dev/xvd"
+  proxmox: "/dev/sd"
+  vmware: "/dev/sd"
+
+# Mountpoints managed by the partitioning role — forbidden for extra disks.
+reserved_mounts:
+  - /boot
+  - /boot/efi
+  - /home
+  - /var
+  - /var/log
+  - /var/log/audit
+
+# Drive letter sequence for disk device naming (max 26 disks).
+disk_letter_map: "abcdefghijklmnopqrstuvwxyz"
+
 system_disk_defaults:
   size: 0
   device: ""