feat(qt): Port win_taskbar_progress to Qt6

[kwsantiago]

Port win_taskbar_progress to Qt6

Ports Windows taskbar progress feature to Qt6 by replacing QtWinExtras (removed in Qt6) with native Windows ITaskbarList3 COM API.

Closes #191

Changes

• Replace QtWinExtras with direct ITaskbarList3 COM interface
• Update depends to build Qt6 (6.7.3)
• Add automatic Qt version detection in depends toolchain
• Add missing libxcb_util_cursor package for Qt6 Linux builds

Implementation

The new WinTaskbarProgress class uses Windows ITaskbarList3 directly, maintaining full feature parity with the Qt5 implementation while working with both Qt5 and Qt6.