pr.tree_ul.expanded_folders references wrong object

[Pluglug]

Overview

editors/base.py:on_pm_rename() uses pr.tree_ul.expanded_folders but this is incorrect.

Problem

• pr.tree_ul returns the PME_UL_pm_tree class, not an instance
• expanded_folders is an instance attribute of TreeState, not a class attribute of PME_UL_pm_tree
• This causes AttributeError: type object 'PME_UL_pm_tree' has no attribute 'expanded_folders'

Current Workaround

Changed to use tree_state.expanded_folders directly (commit pending).

Root Cause

The tree_ul property in preferences.py returns the class itself:

@property
def tree_ul(self):
    return PME_UL_pm_tree

This worked previously because expanded_folders may have been a class attribute, but after the tree.py refactoring it became an instance attribute of TreeState.

Recommended Fix

Either:

1. Remove pr.tree_ul property and use tree_state directly everywhere
2. Or make tree_ul return tree_state instead of the class

Related: Phase 9-X extend_target implementation