Duplicate components from the sheet and tree popups, with links between them

Ctrl+click picks out several boxes on the sheet, and Ctrl/Shift+click several
rows in the tree. Copies are named on from their original (Add1 -> Add2), sit
one step right and down, and keep the links that ran between the copied
components. One undo step; on a device the originals are read back in full
and the copies made there.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

undo.py

@@ -263,6 +263,25 @@ class AddComponentCommand:
             self.parent.insert(self.index, self.element)
 
 
+class CompositeCommand:
+    """Several commands taken as one step, such as a duplicate: its copies and its links.
+
+    Undone last-first, so links go before the components they run between.
+    """
+
+    def __init__(self, commands, label="edit"):
+        self.commands = list(commands)
+        self.label = label
+
+    def undo(self):
+        for command in reversed(self.commands):
+            command.undo()
+
+    def redo(self):
+        for command in self.commands:
+            command.redo()
+
+
 class AddLinkCommand:
     """Adding a single link to the <links> section."""