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.

UI_COMPONENTS_GUIDE.md

@@ -76,6 +76,18 @@ function TaskCard({ task }) {
 </StyledCard>
 ```
 
+### Avatar
+```tsx
+// Avatar avec URL personnalisée
+<Avatar url="https://example.com/photo.jpg" email="user@example.com" name="John Doe" size={64} />
+
+// Avatar Gravatar automatique (si pas d'URL fournie)
+<Avatar email="user@gravatar.com" name="Jane Doe" size={48} />
+
+// Avatar avec fallback
+<Avatar email="unknown@example.com" name="Unknown User" size={32} />
+```
+
 ## 🔄 Migration
 
 ### Étape 1: Identifier les patterns