feat(origin): add interactive open/saveAs methods to SiloOrigin

Add openDocumentInteractive() and saveDocumentAsInteractive() methods
to support the updated FileOrigin interface from Issue #10/#12.

- openDocumentInteractive: Delegates to Silo_Open command for search dialog
- saveDocumentAsInteractive: Triggers new item creation form for Save As

These methods enable the Std_* commands in FreeCAD to delegate to
SiloOrigin when Silo is the active origin.

pkg/freecad/silo_origin.py

@@ -329,6 +329,24 @@ class SiloOrigin:
             FreeCAD.Console.PrintError(f"Silo open item failed: {e}\n")
             return None
 
+    def openDocumentInteractive(self):
+        """Open document interactively via Silo search dialog.
+
+        Shows the Silo_Open dialog for searching and selecting
+        a document to open.
+
+        Returns:
+            Opened App.Document or None
+        """
+        try:
+            cmd = FreeCADGui.Command.get("Silo_Open")
+            if cmd:
+                cmd.Activated()
+            return FreeCAD.ActiveDocument
+        except Exception as e:
+            FreeCAD.Console.PrintError(f"Silo open failed: {e}\n")
+            return None
+
     def saveDocument(self, doc) -> bool:
         """Save document and sync to Silo.
 
@@ -402,6 +420,26 @@ class SiloOrigin:
         )
         return False
 
+    def saveDocumentAsInteractive(self, doc) -> bool:
+        """Save document interactively with new identity.
+
+        For Silo, this triggers the new item creation form which allows
+        the user to select category and create a new part number.
+
+        Args:
+            doc: FreeCAD App.Document
+
+        Returns:
+            True if operation succeeded
+        """
+        if not doc:
+            return False
+
+        # For Silo, "Save As" means creating a new item
+        # Trigger the new item creation form
+        result = self.newDocument()
+        return result is not None
+
     # =========================================================================
     # Extended Operations
     # =========================================================================