feat: enhance avatar handling and update TODO.md

- Added Avatar component with support for custom URLs and Gravatar integration, improving user profile visuals.
- Implemented logic to determine avatar source based on user preferences in profile actions.
- Updated ProfilePage to utilize the new Avatar component for better consistency.
- Marked the integration of Gravatar and custom avatar handling as complete in TODO.md.

src/components/ui-showcase/sections/index.ts

@@ -1,3 +1,4 @@
+export { AvatarSection } from './AvatarSection';
 export { ButtonsSection } from './ButtonsSection';
 export { BadgesSection } from './BadgesSection';
 export { CardsSection } from './CardsSection';