fix(restore-gui): surface registry-backup load failures to the user (#685)

Co-authored-by: Jeffrey <9938813+Raphire@users.noreply.github.com>

Scripts/GUI/Show-RestoreBackupDialog.ps1

@@ -1,3 +1,24 @@
+<#
+    .SYNOPSIS
+        Displays the Restore Backup wizard dialog.
+
+    .DESCRIPTION
+        Presents a modal wizard that lets the user choose and restore either a
+        registry backup or a Start Menu pinned-apps backup. Returns the user's 
+        selection via $window.Tag.
+
+    .PARAMETER Owner
+        Optional parent WPF Window used to host this modal dialog. Defaults to the
+        shared $script:GuiWindow when not supplied.
+
+    .OUTPUTS
+        Hashtable
+        Returns a Hashtable describing the user's choice. Possible shapes:
+          RestoreRegistry  - @{ Result='RestoreRegistry'; Backup=<normalizedBackup> }
+          RestoreStartMenu - @{ Result='RestoreStartMenu'; StartMenuScope=<scope>;
+                               UseManualBackupFile=<bool>; BackupFilePath=<path|string> }
+          Cancelled        - @{ Result='Cancelled' } (from New-RestoreDialogState)
+#>
 function Show-RestoreBackupDialog {
     param(
         [System.Windows.Window]$Owner = $null
@@ -295,9 +316,16 @@ function Show-RestoreBackupDialog {
         }
 
         Write-Host "Backup file selected: $($openDialog.FileName)"
-        $selectedBackup = Load-RegistryBackupFromFile -FilePath $openDialog.FileName
 
-        if (-not (& $showRegistryOverview -SelectedBackup $selectedBackup -SelectedBackupFilePath $openDialog.FileName)) {
+        try {
+            $selectedBackup = Load-RegistryBackupFromFile -FilePath $openDialog.FileName
+
+            if (-not (& $showRegistryOverview -SelectedBackup $selectedBackup -SelectedBackupFilePath $openDialog.FileName)) {
+                return
+            }
+        }
+        catch {
+            Show-MessageBox -Owner $window -Title 'Invalid Backup File' -Message "The selected file could not be loaded:`n$($_.Exception.Message)" -Button 'OK' -Icon 'Error' | Out-Null
             return
         }