Move maximize-hover handling into the snap-assist effect so it can use
the actual decoration button geometry. Render the scene below the picker,
anchor layouts near the cursor, and preview the selected zone without a
fullscreen modal surface.
A normal maximize click keeps priority: hover activation requires a
deliberate pause, dismissal starts a short cooldown, and clicks on the
maximize button still toggle maximize while closing the suggestion.
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.
