feat(core): refactor sidebar header (#6251)

- Add user avatar
- Move sign-out/user settings link from workspace-modal to user avatar modal
- Modify the style of workspace list items
- Modify gap of navigation buttons
- Animate Syncing/Offline/...

![CleanShot 2024-03-22 at 10.22.38.gif](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/LakojjjzZNf6ogjOVwKE/7305f561-a85b-4ec6-89c2-27e2f1b63c85.gif)

packages/frontend/component/src/ui/avatar/style.css.ts

@@ -79,7 +79,6 @@ export const DefaultAvatarContainerStyle = style({
   width: '100%',
   height: '100%',
   position: 'relative',
-  borderRadius: '50%',
   overflow: 'hidden',
 });
 export const DefaultAvatarMiddleItemStyle = style({
@@ -155,6 +154,7 @@ export const avatarFallback = style({
   width: '100%',
   height: '100%',
   borderRadius: '50%',
+  overflow: 'hidden',
   display: 'flex',
   alignItems: 'center',
   justifyContent: 'center',