Add tests for scenery surface caching and preview behavior

- Introduced `test_scenery_brick_preview.gd` to validate focused placement and CPU draw-cost for large brick walls.
- Added `test_scenery_surface_cache.gd` to assess texture budget, visual equivalence, and cache invalidation.
- Created `test_scenery_surface_preview.gd` to evaluate adaptive preview selection and placement behavior.
- Implemented various helper functions to measure drawing performance and validate expected behaviors during tests.
- Added unique identifiers for new test files to ensure proper tracking and management.

tests/test_phase19_surface_followup.gd

@@ -447,7 +447,7 @@ func _test_selector_setup_routes(controller: StageSceneryController) -> void:
 		await process_frame
 		await create_timer(0.2).timeout
 		var ground_ghost: StageRectSurface = controller.get("_ghost") as StageRectSurface
-		_expect(ground_ghost != null and ground_ghost.panel_size.is_equal_approx(Vector2(800.0, 320.0)), "background-ground placement displays its patterned cursor ghost after production mouse motion")
+		_expect(ground_ghost != null and ground_ghost.panel_size.is_equal_approx(Vector2(240.0, 280.0)), "background-ground placement starts with a cursor ghost the same size as a wall panel")
 		_capture_root_viewport("phase19_ground_placement.png")
 	controller.exit_tool()
 	selector.hide()