Add multi-level stacking support for trays

Add multi-notch support: N/S/W/E checkboxes replace single dropdown

Merge pull request #2 from andrelimafalcao/feature/toolbar-icons-window-controls

Apply canvas tray colors to generated FreeCAD geometry

Make folder icon taller (top from y=10 to y=7)

Redesign load/save icons: open folder and diskette, no arrows

Redesign undo/redo icons as return-style arrows

Enlarge undo/redo icons: radius 11, stroke-width 3 for better visibility

Redesign undo/redo icons as circular sweep arrows

Fix separator detection: use type() check instead of missing fixedWidth()

Fix toolbar separators: use QWidget with background color, add spacing

Increase toolbar buttons to 36x36, sharper separators

Switch toolbar buttons to QToolButton to enforce compact fixed size

Reduce toolbar button size to 26×26 with 16×16 icons

Toolbar icons-only with tooltips, separators, and window min/max buttons