feat: Implement Phase 4 Trigger Events System

- Added a new event-driven system for reactive storytelling, allowing rules like "When X happens, do Y."
- Introduced TriggerArea class for placeable sensors in the stage.
- Enhanced StickmanRig to emit signals for actions and arrivals.
- Updated StageDirectorVisuals to render rules visually with labels and badges.
- Modified StageSpawner to support spawning TriggerAreas.
- Improved text baseline calculations in speech bubbles and rule labels.
- Added tests for text baseline fixes to ensure proper rendering.
- Documented the implementation plan for Phase 4 in PHASE_4_TRIGGER_EVENTS.md.
- Created a polish plan for Phase 4 in PHASE_4b_POLISH.md.

scripts/stage_spawner.gd

@@ -15,6 +15,7 @@ const TERRAIN_UTILS := preload("res://scripts/terrain_utils.gd")
 const PROP_UTILS := preload("res://scripts/prop_utils.gd")
 const PROP_BLOCK := preload("res://scripts/prop_block.gd")
 const STICKMAN_FACTORY := preload("res://scripts/stickman_factory.gd")
+const TRIGGER_AREA := preload("res://scripts/trigger_area.gd")
 
 # ---------------------------------------------------------------------------
 # Constants
@@ -87,6 +88,8 @@ func spawn(id: String, world_position: Vector2) -> Node2D:
 			return _spawn_prop(entry, pos)
 		"stickman":
 			return _spawn_stickman(pos)
+		"area":
+			return _spawn_area(pos)
 		_:
 			push_warning("StageSpawner: unknown spawn kind '%s'." % entry.get("kind", ""))
 			return null
@@ -98,6 +101,9 @@ func spawn(id: String, world_position: Vector2) -> Node2D:
 static func get_world_aabb(node: Node2D) -> Rect2:
 	if node == null or not is_instance_valid(node):
 		return Rect2()
+	# Duck-typed TriggerArea: expose its centered local rect through the transform.
+	if node.has_method("get_area_rect"):
+		return node.global_transform * (node.call("get_area_rect") as Rect2)
 	var poly := node.get_node_or_null(NodePath("Polygon2D")) as Polygon2D
 	if poly != null and not poly.polygon.is_empty():
 		var rect := Rect2(node.to_global(poly.polygon[0]), Vector2.ZERO)
@@ -174,6 +180,10 @@ func _build_registry() -> void:
 			"id": "stickman", "label": "Stickman", "kind": "stickman",
 			"spawn_offset": STICKMAN_FOOT_OFFSET,
 		},
+		{
+			"id": "area", "label": "Area", "kind": "area",
+			"spawn_offset": Vector2.ZERO,
+		},
 	]
 
 
@@ -213,6 +223,14 @@ func _spawn_prop(entry: Dictionary, world_position: Vector2) -> PropBlock:
 	return PROP_UTILS.spawn_prop(_world, world_position, payload, preset, Vector2.ZERO)
 
 
+func _spawn_area(world_position: Vector2) -> Node2D:
+	var area: Node2D = TRIGGER_AREA.new()
+	area.name = "TriggerArea"
+	area.position = world_position
+	_world.add_child(area)
+	return area
+
+
 func _spawn_stickman(world_position: Vector2) -> StickmanRig:
 	if _stickman_data.is_empty():
 		push_warning("StageSpawner: no stickman data loaded; check '%s'." % DEFAULT_STICKMAN_PATH)