fix: use FreeCADGui.Document.Modified instead of App.Document.IsModified()

App.Document has no IsModified() method, causing Silo_Pull to crash with
AttributeError. The correct API is to get the Gui document and check its
Modified property, consistent with the pattern used elsewhere in this file
(lines 891, 913).

freecad/silo_commands.py

@@ -990,8 +990,10 @@ def _check_pull_conflicts(part_number, local_path, doc=None):
     conflicts = []
 
     # Check for unsaved changes in an open document
-    if doc is not None and doc.IsModified():
-        conflicts.append("Document has unsaved local changes.")
+    if doc is not None:
+        gui_doc = FreeCADGui.getDocument(doc.Name) if doc.Name else None
+        if gui_doc and gui_doc.Modified:
+            conflicts.append("Document has unsaved local changes.")
 
     # Check local revision vs server latest
     if doc is not None: