Graph Editor: Add backdrop button to navigation toolbar with selection-aware creation

[Copilot]

Description

Adds a sticky_note_2 icon button to the Graph Editor's bottom-left navigation toolbar to create Backdrop nodes. When nodes are selected, the backdrop is sized and positioned to wrap around them; otherwise it is created at the viewport center. The create+resize operation produces a single undo stack entry.

Features list

• Add "Add Backdrop" (sticky_note_2) button to the Graph Editor navigation toolbar
• When nodes are selected, create the backdrop around their bounding box (with gridSpacing padding on all sides)
• When no nodes are selected, create backdrop at viewport center with default size
• Single undo stack entry for the combined create+resize operation

Implementation remarks

Bounding box uses node.nodeWidth/nodeHeight, falling back to uigraph.layout.nodeWidth/nodeHeight (160×120) for regular nodes whose size properties return 0. Padding uses uigraph.layout.gridSpacing (40px) for consistency with the layout system.

A new addBackdropNode(position, width, height) slot was added to UIGraph in graph.py. It uses groupedGraphModification to wrap node creation and nodeWidth/nodeHeight attribute setting atomically — avoiding the nested macro that would result from calling resizeNode (which already wraps itself):

@Slot(QPoint, int, int, result=QObject)
def addBackdropNode(self, position, width, height):
    with self.groupedGraphModification("Add Backdrop"):
        node = self.addNewNode("Backdrop", position)
        if node.hasInternalAttribute("nodeWidth"):
            self.setAttribute(node.internalAttribute("nodeWidth"), width)
        if node.hasInternalAttribute("nodeHeight"):
            self.setAttribute(node.internalAttribute("nodeHeight"), height)
    return node

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.99%. Comparing base (43a24bb) to head (d5a348a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3011   +/-   ##
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  Coverage    81.99%   81.99%           
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  Files           69       69           
  Lines         9315     9315           
========================================
  Hits          7638     7638           
  Misses        1677     1677           

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