Project Tree

QAbstractItemModel-based tree view for the planning hierarchy.

Key Classes

Class	Purpose
PlanningTreeModel	QAbstractItemModel backed by PlanningController
PlanningTreeNodes	Internal tree node objects for the model
StrukturFilterProxy	QSortFilterProxyModel for Struktur-only filtering
ProjectTreeWidget	QWidget wrapper owning model, view, and delegate
ProjectTreeDelegate	Custom delegate for icons, status colors, lock indicators
FluentTreeProxyStyle	QProxyStyle for chevron branch rendering

Signals (from ProjectTreeWidget)

• item_selected, item_double_clicked -- selection events
• item_drop_requested, item_reorder_requested -- internal drag-drop
• library_item_drop_requested -- external library item drops
• context_menu_requested, rename_requested, delete_requested -- CRUD
• copy_requested, paste_requested, save_requested -- keyboard shortcuts
• undo_requested, redo_requested -- undo/redo shortcuts
• expand_all_requested, collapse_all_requested -- hotkey-driven

Notes

• Uses incremental updates via controller signals (not full rebuild)
• Supports multi-select for copy/paste operations
• Drop indicator rendering handles both internal and library drops