fix: handle undefined user name in UI components

- Added null check in getUserInitials function to return "??" for undefined names
- Fixed logout button to handle undefined user.name when displaying first name
- Prevents 500 errors when rendering components for users without names

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/frontend/src/lib/utils.ts

@@ -27,6 +27,7 @@ export const calcReadingTime = (text: string) => {
 };
 
 export const getUserInitials = (name: string) => {
+	if (!name) return "??";
 	return name
 		.split(" ")
 		.map((word) => word.charAt(0))