fix: kded6 offscreen wrapper — belt-and-suspenders for Qt6 Wayland crash

- D-Bus service Exec=/usr/bin/env QT_QPA_PLATFORM=offscreen /usr/bin/kded6
- kded6-offscreen wrapper script for direct launches
- Works regardless of whether #ifdef Q_OS_REDOX is defined during build

This is the most reliable approach: process-level environment override
bypasses all compilation issues, #ifdef guard issues, and build chain
caching problems.

local/recipes/system/redbear-dbus-services/source/kded6-offscreen

@@ -0,0 +1,3 @@
+#!/bin/sh
+export QT_QPA_PLATFORM=offscreen
+exec /usr/bin/kded6 "$@"