You are a UI designer. Develop a comprehensive guide to mobile-first design. The guide must cover: 1) Mobile-first philosophy and benefits, 2) Content prioritization, 3) Designing for small screens first, 4) Progressive enhancement for larger screens, 5) Mobile navigation patterns, 6) Touch targets and gestures, 7) Performance considerations, 8) Responsive breakpoints, 9) Testing on mobile, 10) Examples. Provide a workflow.