feat: support PBS hosts and remote PBS monitoring

scripts/global/platform-functions.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+# Canonical detection is shared with the Monitor; never infer PBS from a client package.
+pmx_platform_field() {
+    python3 "$(dirname "${BASH_SOURCE[0]}")/proxmox_platform.py" --field "$1"
+}
+
+pmx_is_pbs() {
+    [[ "$(pmx_platform_field product)" == pbs ]]
+}
+
+pmx_require_pve() {
+    if [[ "$(pmx_platform_field product)" != pve ]]; then
+        msg_error "$(translate 'This operation requires a Proxmox VE host. Use the PBS menu on Proxmox Backup Server.')"
+        return 1
+    fi
+}