fix(UX): offer registration when BOM opened on untracked document (#56)

Replace the dead-end warning in Silo_BOM with a question dialog that
offers to register the document via Silo_New. If the user accepts and
registration succeeds, the BOM dialog opens seamlessly.

freecad/silo_commands.py

@@ -1998,15 +1998,18 @@ class Silo_BOM:
 
         obj = get_tracked_object(doc)
         if not obj:
-            FreeCAD.Console.PrintError("No tracked Silo item in active document.\n")
-            from PySide import QtGui as _qg
-
-            _qg.QMessageBox.warning(
+            reply = QtGui.QMessageBox.question(
                 None,
                 "BOM",
-                "This document is not registered with Silo.\nUse Silo > New to register it first.",
+                "This document is not registered with Silo.\n\nRegister it now?",
+                QtGui.QMessageBox.Yes | QtGui.QMessageBox.No,
             )
-            return
+            if reply != QtGui.QMessageBox.Yes:
+                return
+            FreeCADGui.runCommand("Silo_New")
+            obj = get_tracked_object(doc)
+            if not obj:
+                return
 
         part_number = obj.SiloPartNumber