Set the project's frame shape: one of 16:9, 9:16, 2.39:1, 4:3, 3:4. A project needs one before storyboard work: create_shots refuses while get_project_outline shows aspectRatio null. Ask the user which ratio they want; do not pick one for them. Shots created afterwards use it for their storyboard and production frames; existing shots keep the ratio they were created with. Returns aspectRatio and previousAspectRatio (null when it was unset).