Fix blur in Dolphin settings and properties dialogs

[TchelloSimis]

Summary

• request a blur region for Dolphin settings and properties dialogs
• keep the existing specialized handling for About dialogs unchanged
• limit the new behavior to Dolphin, without changing other applications

Problem

When Darkly's translucent colors or opacity settings are used, Dolphin's main window is blurred correctly, but its Configure dialog is only transparent. The wallpaper and windows behind it remain sharp.

blurSettingsDialogRegion() currently accepts only KAboutApplicationDialog and KDEPrivate::KAboutKdeDialog, so a normal Dolphin dialog produces no blur region for KWin.

Change

For non-About dialogs in Dolphin, request blur for the full client area. Opaque pixels remain visually unaffected, while translucent panels receive the expected compositor blur. About dialogs continue through their existing tab-specific path.

Verification

• reproduced with Plasma 6.6.4 on Wayland and Dolphin 25.12.3
• manually verified that Dolphin's Configure dialog changes from transparency-only to transparency with blur
• built the complete project with both Qt 5 and Qt 6 enabled
• ran all six bundled Qt 5/Qt 6 test executables: 40 passed, 0 failed

Thank you for maintaining Darkly.