Design user flows, wireframes, and screen lists based on product requirements. Use as step 4 of the
product pipeline, after product requirements are complete. Requires `03-product-requirements.md` as
input. Produces user flows, wireframe descriptions, and a comprehensive screen list.
Examples:
- user: "Design the UX" → create user flows and wireframes
- user: "Step 4 of the pipeline" → load requirements and design UX
