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

Scene.gd

@@ -128,7 +128,12 @@ func _unhandled_input(event):
 		if ScriptBuilder.current_script and not ScriptBuilder.current_script.can_interrupt:
 			if ScriptBuilder.current_script.handle_input(event):
 				return
-		
+
+		# Block input when inventory overlay is active
+		var overlay = get_node_or_null("/root/Node2D/InventoryOverlay")
+		if overlay and overlay is InventoryOverlay and overlay.is_active():
+			return
+
 		var root = get_node("/root/Node2D")
 		# If look cursor is active and we got here, no SetPiece handled the input
 		# so this is a room-wide look
@@ -138,7 +143,46 @@ func _unhandled_input(event):
 		if ActionState.current_action == ActionState.Action.WALK:
 			var path = NavigationServer2D.map_get_path(map, ego.position, pathfind.to_local(get_global_mouse_position()), true)
 			start_main_script(ScriptBuilder.init(ScriptBuilder.walk_path(ego, path)).can_interrupt().build(self, "_on_script_complete"))
+		if ActionState.current_action == ActionState.Action.ITEM:
+			_on_item_use_in_world()
 
 func _on_room_looked() -> void:
 	# Default room look description - override in room scripts
 	pass
+
+func _on_item_use_in_world() -> void:
+	if not InventoryManager.selected_item:
+		return
+	var item_id = InventoryManager.selected_item
+	var top_piece = ActionState.get_top_hovered_setpiece()
+	if top_piece:
+		_use_item_on_setpiece(item_id, top_piece)
+	else:
+		_on_item_used_empty_space(item_id)
+
+func _use_item_on_setpiece(item_id: String, piece: SetPiece) -> void:
+	if piece.has_method("_on_item_used"):
+		piece._on_item_used(item_id)
+	else:
+		var def = InventoryManager.get_item_definition(item_id)
+		var item_name = item_id
+		if def:
+			item_name = def.name
+		var piece_name = piece.label if piece.label else piece.name
+		start_main_script(ScriptBuilder.init(ScriptBuilder.say(ego, "I can't use the %s on the %s." % [item_name, piece_name])).build(self, "_on_script_complete"))
+
+func _on_item_used_empty_space(item_id: String) -> void:
+	var def = InventoryManager.get_item_definition(item_id)
+	var item_name = item_id
+	if def:
+		item_name = def.name
+	start_main_script(ScriptBuilder.init(ScriptBuilder.say(ego, "There's nothing to use the %s on here." % [item_name])).build(self, "_on_script_complete"))
+
+func give_item(item_id: String) -> void:
+	InventoryManager.acquire_item(item_id)
+
+func remove_item(item_id: String, quiet: bool = false) -> void:
+	InventoryManager.remove_item(item_id, quiet)
+
+func strip_items(event_items: Array[String], exempt_items: Array[String] = []) -> void:
+	InventoryManager.bulk_strip_items(event_items, exempt_items)