In QCAD 3.32.9.0 with Qt 6.11.0, the presence of QTreeView::item:hover rule (even empty) in Heather theme's CSS causes the layer list to change the active layer on mouse hover, without clicking.

Heather theme has QTreeView::item:hover by default → Bug occurs
Dark theme has no QTreeView::item:hover → Normal behavior
Custom CSS with ONLY QTreeView::item:hover {} → Bug occurs

This did NOT occur in Qt5 production versions.

Reproduction Steps:
1. Apply Heather theme (contains QTreeView::item:hover by default)
2. OR: Apply any theme + add ONLY this CSS rule:

 QTreeView::item:hover {
 }

3. Restart QCAD as prompted after theme modification
4. Open layer list panel
5. Hover mouse over any layer item → Active layer immediately switches to hovered layer

Expected Behavior:
- Hover should only affect visual appearance
- Active layer should only change on explicit click selection
- Empty CSS rule "{}" should have no functional effect

Actual Behavior:
- Every layer becomes active as mouse hovers over it
- Affects ALL layers in layer list
- Property editor QTreeView and block list QTreeView are NOT affected

Workaround:
- Remove QTreeView::item:hover rule completely from CSS
- Use themes without QTreeView::item:hover (e.g., Dark theme)

Environment:
- QCAD: 3.32.9.0
- Qt: 6.11.0
- OS: Windows 11 25H2 (Build 26200.8328)
- Trigger: Heather theme OR any theme + QTreeView::item:hover CSS rule