The decoration QML sandbox has no DBus or kglobalaccel access, so
the Qt.callDBus call from the maximize-button hover Timer was a
silent no-op. Remove the dead Timer, hover state and grid-dot
overlay; the shift-tiling script now polls the cursor over the
title-bar button strip and triggers SHIFT Snap Assist itself.
Also refresh the SPDX header on both decoration files.
Add a KWin decoration package under kwin/decorations and install it
into share/kwin/decorations. The QML theme defines Shift titlebar
colors, button rendering, and maximized border geometry.
Wire the new decorations subdirectory from kwin/CMakeLists.txt.
