fix: defer PartDesign manipulator registration until commands are imported

The _ZToolsPartDesignManipulator was registered at module load time via
Gui.addWorkbenchManipulator(), but the commands it references
(ZTools_DatumCreator, ZTools_DatumManager, ZTools_EnhancedPocket,
ZTools_RotatedLinearPattern) are not registered until Initialize()
imports the command modules.

Move the addWorkbenchManipulator() call into Initialize() with a guard
to prevent duplicate registration. This eliminates the 'Unknown command'
warnings on startup.

ztools/InitGui.py

@@ -306,6 +306,12 @@ class ZToolsWorkbench(Gui.Workbench):
             + self.ztools_spreadsheet_tools,
         )
 
+        # Register the PartDesign manipulator now that commands exist.
+        # Guard so it only registers once even if Initialize is called again.
+        if not getattr(ZToolsWorkbench, "_manipulator_installed", False):
+            ZToolsWorkbench._manipulator_installed = True
+            Gui.addWorkbenchManipulator(_ZToolsPartDesignManipulator())
+
         App.Console.PrintMessage("ztools workbench initialized\n")
 
     def Activated(self):
@@ -334,6 +340,8 @@ Gui.addWorkbench(ZToolsWorkbench())
 # ---------------------------------------------------------------------------
 # WorkbenchManipulator: inject ZTools commands into PartDesign workbench
 # ---------------------------------------------------------------------------
+# Registered in ZToolsWorkbench.Initialize() after commands are imported,
+# so the commands exist before the manipulator references them.
 
 
 class _ZToolsPartDesignManipulator:
@@ -376,6 +384,3 @@ class _ZToolsPartDesignManipulator:
                 "after": "",
             },
         ]
-
-
-Gui.addWorkbenchManipulator(_ZToolsPartDesignManipulator())