Align lock toolbar menu button on Windows

[TurboTheTurtle]

Closes #24498.

Applies a Windows-only toolbar button style adjustment so the lock action menu indicator is positioned inside the lock button while keeping the existing lock and menu behavior unchanged.

Testing

• CI: all GitHub checks pass, including the Windows builds from run 27494277364.
• Manual Windows proof: launched the PR-head Windows CI artifact on Windows 11 with an isolated profile and Style=windows, ColorScheme=Dark.
• Confirmed the qBittorrent window opens in the dark Windows style.
• Confirmed the top toolbar lock dropdown arrow renders inside the lock button bounds, aligned on the right side of the button.
• Confirmed clicking the lock dropdown arrow opens the existing menu with Set Password and Clear Password.

Screenshot