Fix multi-selected desktop icons only ever dragging one at a time

Reported live: "try move desktop items all at once somewhere else"
didn't work. Two compounding bugs, both real: CompState::
desktop_icon_drag only ever tracked one icon id, and the click handler
that starts a drag unconditionally collapsed any existing multi-
selection down to just the grabbed icon before the drag even began.

desktop_icon_drag is now Option<DesktopIconDrag> (crates/wayland/src/
desktop_icons.rs, new type): a grab offset, the grabbed icon's own live
position, and a members list - every currently-selected icon (the
grabbed one included), each a fixed offset from the grabbed icon's own
top-left at drag start, so the group moves as one rigid unit.
input/pointer.rs's click handler now only resets to single-selection
when the grabbed icon isn't already part of the current selection --
grabbing one inside an existing multi-selection keeps the whole group
selected and dragging, matching Windows/GNOME/macOS/KDE convention.
end_desktop_icon_drag snaps every dragged icon to its own nearest free
grid cell independently, tracking newly-claimed cells across the group
so two icons landing near each other never claim the same one.

Full workspace build/test/clippy clean, built and installed. Not unit-
testable (this module has no CompState test fixture for its own
selection/drag logic, an already-documented, accepted gap) - needs a
live drag to confirm.

0 files changed, 0 insertions, 0 deletions