feat: integrate inventory with cursor system, scene input, and GameScript

- ActionState: add ITEM action (value 4) to enum and get_action_name()
- MainGame: right-click cycles through all 5 actions including ITEM;
  skips ITEM if nothing selected; clears selection when cycling away
- Scene: guard _unhandled_input() against active inventory overlay;
  handle ITEM action for world-wide item use; add give_item(),
  remove_item(), strip_items() helper methods
- SetPiece: handle ITEM action by calling scene's _use_item_on_setpiece()
- GameScript: add GiveItem and GiveItemDeferred script step classes
  for item acquisition during cutscenes

GameScript.gd

@@ -476,5 +476,54 @@ func switch_camera(path):
 func reset_camera():
 	var thing = ResetCamera.new()
 	return thing
+
+class GiveItem:
+	extends ScriptNode
+	var item_id: String = ""
+	var text: String = ""
+	var subject: Node2D = null
+	var done = false
+	var started = false
+
+	func step_type():
+		return "GiveItem " + item_id
+
+	func init(scene):
+		super(scene)
+
+	func do(delta):
+		if not started:
+			started = true
+			if text:
+				await scene.find_child("dialogue").say(text)
+			InventoryManager.acquire_item(item_id)
+			done = true
+
+	func is_done():
+		return done
+
+	func interrupt():
+		done = true
+
+class GiveItemDeferred:
+	extends GiveItem
+	var subject_name: String = ""
+
+	func init(scene):
+		super(scene)
+		subject = scene.get_node(subject_name)
+
+func give_item(item_id: String, text: String = ""):
+	var step = GiveItem.new()
+	step.item_id = item_id
+	step.text = text
+	return step
+
+func give_item_deferred(item_id: String, subject_name: String, text: String = ""):
+	var step = GiveItemDeferred.new()
+	step.item_id = item_id
+	step.subject_name = subject_name
+	step.text = text
+	return step
 	
 var current_script : ScriptGraph = null