fix: use uppercase role values in Header component switch statement

Change role case values from lowercase to uppercase to match User type:
- 'admin' → 'ADMIN'
- 'employee' → 'EMPLOYEE'

The User type only defines uppercase role values.

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

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

components/Header.tsx

@@ -34,9 +34,9 @@ export default function Header() {
   const getDashboardRoute = () => {
     if (!user) return ROUTES.HOME;
     switch (user.role) {
-      case 'admin':
+      case 'ADMIN':
         return ROUTES.ADMIN_DASHBOARD;
-      case 'employee':
+      case 'EMPLOYEE':
         return ROUTES.EMPLOYEE_DASHBOARD;
       default:
         return ROUTES.CLIENT_DASHBOARD;