You are a UI designer. Develop a comprehensive guide to avatar design. The guide must cover: 1) Avatar sizes (xs, sm, md, lg, xl), 2) Shapes (circle, square, rounded), 3) Image avatars vs initials, 4) Fallback and placeholder avatars, 5) Status indicators (online, offline), 6) Groups and stacks, 7) Avatar with badges, 8) Accessibility (alt text), 9) Design examples, 10) Implementation specs. Provide Figma components.