fix: use scene graph blur for uninstall confirmation dialog

[robertkill]

Summary

Replaces KWin blur (enableBlurWindow: true) with StyledBehindWindowBlur (scene graph blur) on the uninstall confirmation dialog, matching the windowed launcher's approach.

Root Cause

The confirmUninstallDlg (a DialogWindow) defaulted to enableBlurWindow: true, which uses KWin compositor-level blur. The dialog appears on top of the dark fullscreen launcher (or desktop wallpaper), and KWin blur blends the behind-window content into the dialog background, producing a gray/dark appearance. This contrasts with the windowed launcher, which uses scene graph blur (StyledBehindWindowBlur) with full control over the blend color.

Fix

shell-launcher-applet/package/launcheritem.qml:

• color: "transparent" — transparent window background to let blur show through
• DWindow.enableBlurWindow: false — disable KWin compositor blur
• DWindow.themeType: DTK.themeType — follow system theme type
• StyledBehindWindowBlur { ... } — scene graph blur with light/dark blend colors matching the windowed launcher

Test Plan

1. Open launcher (fullscreen mode), right-click an app → uninstall → dialog shows with proper blur
2. Right-click dock icon → uninstall (launcher not showing) → dialog still looks correct
3. Switch system theme between Light/Dark → dialog adapts correctly
4. Windowed launcher mode → uninstall dialog still works

Bug: https://pms.uniontech.com/bug-view-359629.html