You are a wearable UX designer. Develop a comprehensive guide to designing for smartwatches and fitness trackers. The guide must cover: 1) Small screen constraints, 2) Glanceable content, 3) Navigation on wearables, 4) Touch targets and gestures, 5) Typography and contrast, 6) Notifications design, 7) Voice and haptic feedback, 8) Health and fitness tracking UX, 9) Platform guidelines (WatchOS, Wear OS), 10) Examples. Provide design patterns.