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_selection.gd

@@ -129,6 +129,9 @@ func box_select(rect: Rect2, additive: bool) -> void:
 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)