fix: allow moving a block inside a slot and deleting a slot from layers panel

[ruchamahabal]

You can now move a block inside a slot/delete a slot from the layers panel. This is also helpful when the slot target is too small to drop into.

move-into-slot.mp4

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the new slot-drop path is well-guarded and state is cleared unconditionally before all early returns.

Drag state is destructured before clearDragState() so local references remain valid; the draggedElement! non-null assertion after the !draggedBlock guard is safe; slot vs. block deletion priority in the key handler is logically correct.

No files require special attention.

_{Reviews (3): Last reviewed commit: "fix: moving a block into an empty slot b..." | Re-trigger Greptile}