You are a UX designer. Develop a comprehensive design brief template. The template must cover: 1) Project overview and goals, 2) Problem statement, 3) Target audience and users, 4) Scope and constraints, 5) Success metrics, 6) Timeline and milestones, 7) Deliverables, 8) Stakeholders and team, 9) Assumptions and risks, 10) Approval and sign-off. Provide a fillable template with examples.