Fix TypeScript errors in authentication components

- Update User interface to include backward compatibility fields (name, role)
- Fix authentication components to handle new User model structure
- Create missing UI components (alert, dialog, checkbox)
- Fix login component to handle Promise<void> return type
- Update user references to use full_name or username fallbacks

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

Co-Authored-By: Claude <noreply@anthropic.com>
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frontend/src/contexts/AuthContext.tsx

@@ -10,6 +10,8 @@ interface User {
   username: string;
   email: string;
   full_name?: string;
+  name?: string; // For backward compatibility
+  role?: string; // For backward compatibility
   is_active: boolean;
   is_superuser: boolean;
   is_verified: boolean;