feat: Enhance Trigger Area Reliability in Sandbox Stage

- Updated `_rule_matches` to ensure `entered_area` checks both source and target instance IDs for accurate event triggering.
- Refined `_update_area_entry` to utilize `_movable_overlaps_area`, ensuring that visible stickman/prop geometry is considered for area overlap detection.
- Introduced a new regression test suite in `tests/test_phase4c_area.gd` to validate the functionality of `entered_area` rules, covering various edge cases and ensuring correct behavior for source-specific and wildcard rules.
- Documented the architectural changes and validation results in `specs/phase_4c_area.md`, detailing the scope, data contracts, and design decisions made during implementation.
- Added new agent configurations for architect, developer, and writer roles to streamline the development process and improve documentation practices.

scripts/sandbox_stage.gd

@@ -2436,7 +2436,7 @@ func _rule_matches(rule: Dictionary, event: Dictionary) -> bool:
 		"speech_finished":
 			return _ids_match(source_id, source)
 		"entered_area":
-			return _ids_match(target_id, target)
+			return _ids_match(source_id, source) and _ids_match(target_id, target)
 		"collided":
 			return _ids_match(source_id, source) and _ids_match(target_id, target)
 		_:
@@ -2492,7 +2492,7 @@ func _update_area_entry() -> void:
 		for node: Node2D in movables:
 			var point := _movable_point(node)
 			var key := "%d:%d" % [area.get_instance_id(), node.get_instance_id()]
-			var inside: bool = area_rect.has_point(point)
+			var inside: bool = _movable_overlaps_area(node, area_rect)
 			var was: bool = bool(_area_overlap.get(key, false))
 			if inside and not was:
 				_area_overlap[key] = true
@@ -2533,6 +2533,18 @@ func _movable_point(node: Node2D) -> Vector2:
 	return node.global_position
 
 
+## Trigger entry follows the visible object, not only its origin/feet anchor.
+## StageSelection already owns the mounted-geometry world AABB contract used by
+## selection and gizmos, so reuse it here to keep what the user sees and what
+## the event engine detects in agreement. Point-like fallbacks retain the old
+## behavior for any future movable without visual bounds.
+func _movable_overlaps_area(node: Node2D, area_rect: Rect2) -> bool:
+	var bounds := STAGE_SELECTION.get_world_aabb(node).abs()
+	if bounds.size.is_zero_approx():
+		return area_rect.has_point(_movable_point(node))
+	return area_rect.intersects(bounds, true)
+
+
 func _show_toast(msg: String) -> void:
 	_toast_text = msg
 	_toast_timer = 2.0