Keep "Collapse Menu" visible (disabled) in edit mode to prevent layout jump

[chriskmnds]

Overview

Entering edit mode should not remove the Collapse Menu item from the sidebar. Keep it in place and render it in a disabled state so the layout does not jump.

Behavior

• Trigger: edit mode is active.
• The Collapse Menu item stays in its current position.
• It is rendered as disabled, for example with reduced opacity, so it is clearly not interactive while editing.
• Users can still drop plugins below Collapse Menu.
• When edit mode exits, Collapse Menu returns to its normal interactive state.

Why

Removing Collapse Menu shifts every item below it, which is jarring and breaks spatial memory. Keeping the item in place preserves layout stability while making it clear that the control is temporarily unavailable.