Implement Phase 10a - Prop Scaling

- Added specifications for Phase 10a, introducing permanent size changes to `.prop` documents and reversible uniform instance scaling in Sandbox EDIT mode.
- Updated `PropCanvas`, `PropAnchorData`, `PropEditor`, `StageGizmos`, `SandboxStage`, and `StageSelection` classes to support new scaling features.
- Implemented document transactions for scaling, including normalization to a 96 px maximum dimension.
- Introduced a new **Transform Whole Prop** tool in the Prop Editor for moving, rotating, and resizing props.
- Created unit tests for the new scaling functionality, validating shape scaling, anchor transformations, and whole-prop interactions.
- Ensured compatibility with existing prop formats and maintained the integrity of the document structure during scaling operations.

scripts/prop_block.gd

@@ -95,6 +95,9 @@ var _collision_shape: CollisionShape2D
 var _circle_shape: CircleShape2D
 var _custom_shapes: bool = false
 var _visual_local_bounds := Rect2()
+var _custom_collision_hull: PackedVector2Array = PackedVector2Array()
+var _play_instance_scale: Vector2 = Vector2.ONE
+var _play_scale_active: bool = false
 
 # ---------------------------------------------------------------------------
 # Signals
@@ -257,7 +260,8 @@ func set_custom_shapes(shapes: Array[Dictionary], collision_hull: PackedVector2A
 	_outline.visible = false
 	_set_collision_shape_enabled(false)
 	_set_collision_polygon_enabled(true)
-	_collision_polygon.polygon = collision_hull
+	_custom_collision_hull = collision_hull.duplicate()
+	_collision_polygon.polygon = _custom_collision_hull
 	var visuals := get_node_or_null(NodePath("Visuals")) as Node2D
 	if visuals == null:
 		visuals = Node2D.new(); visuals.name = "Visuals"; add_child(visuals)
@@ -273,6 +277,67 @@ func has_custom_shapes() -> bool:
 func get_visual_local_bounds() -> Rect2:
 	return _visual_local_bounds
 
+## RigidBody2D transforms do not reliably retain scale during simulation. Move
+## the authored uniform scale into child visuals and collision geometry for
+## PLAY, then restore the root scale on return to EDIT for scene persistence.
+func begin_play_instance_scale() -> void:
+	if _play_scale_active:
+		return
+	_play_instance_scale = scale
+	if _play_instance_scale.is_equal_approx(Vector2.ONE):
+		return
+	_play_scale_active = true
+	scale = Vector2.ONE
+	_apply_play_scale()
+
+func end_play_instance_scale() -> void:
+	if not _play_scale_active:
+		return
+	_play_scale_active = false
+	_set_visual_scale(Vector2.ONE)
+	_apply_shape()
+	if _custom_shapes and _collision_polygon != null:
+		_collision_polygon.polygon = _custom_collision_hull
+	scale = _play_instance_scale
+
+func _apply_play_scale() -> void:
+	_set_visual_scale(_play_instance_scale)
+	if _custom_shapes:
+		if _collision_polygon != null:
+			_collision_polygon.polygon = _scaled_points(_custom_collision_hull, _play_instance_scale)
+		return
+	if shape_type == ShapeType.CIRCLE:
+		# A non-uniform legacy instance scale makes an ellipse. Use the generated
+		# polygon hull while simulating so collision follows both axes exactly.
+		if _collision_polygon != null:
+			_collision_polygon.polygon = _scaled_points(_circle_loop(), _play_instance_scale)
+		_set_collision_shape_enabled(false)
+		_set_collision_polygon_enabled(true)
+	elif _collision_polygon != null:
+		_collision_polygon.polygon = _scaled_points(polygon_points, _play_instance_scale)
+
+func _set_visual_scale(value: Vector2) -> void:
+	if _polygon != null:
+		_polygon.scale = value
+	if _outline != null:
+		_outline.scale = value
+	var visuals: Node2D = get_node_or_null(NodePath("Visuals")) as Node2D
+	if visuals != null:
+		visuals.scale = value
+
+func _scaled_points(points: PackedVector2Array, value: Vector2) -> PackedVector2Array:
+	var result: PackedVector2Array = PackedVector2Array()
+	for point: Vector2 in points:
+		result.append(point * value)
+	return result
+
+func _circle_loop() -> PackedVector2Array:
+	var result: PackedVector2Array = PackedVector2Array()
+	for index: int in CIRCLE_SEGMENTS:
+		var angle: float = TAU * float(index) / float(CIRCLE_SEGMENTS)
+		result.append(Vector2(cos(angle), sin(angle)) * radius)
+	return result
+
 # ---------------------------------------------------------------------------
 # Static preset factories
 # ---------------------------------------------------------------------------