The task panel window reserved bottom-edge screen space even
with zero thickness and invisible content. Set its visibility
mode to auto-hide in convergence and force the dock bottom
margin to zero so the favourites bar sits flush at the screen
edge.
Halve the favourites bar from gridUnit*6 to gridUnit*3 to avoid
oversized dock on desktop screens. Hide the arrow-up icon and
disable the page-indicator tap handler since the app drawer is
now opened via the dedicated Overview button.
This refactors the homescreen state object to isolate drag & drop from
swipe states, allowing for using proper system-level drag & drop for delegate
movement. This then ports the new applet list to use it.
