debug: add logging to inventory overlay and backpack for click debugging

inventory/inventory_overlay/InventorySlot.gd

@@ -35,8 +35,10 @@ func set_hover(hovered: bool) -> void:
 			item_box.color = Color(0.8, 0.8, 0.8, 1)
 
 func _gui_input(event: InputEvent) -> void:
+	print("[SLOT:%s] _gui_input: %s" % [item_id, event])
 	if event is InputEventMouseButton:
 		if event.button_index == 1 and event.pressed:
+			print("[SLOT:%s] emitting clicked" % item_id)
 			clicked.emit(item_id)
 		elif event.button_index == 2:
 			right_clicked.emit(item_id)