Dropdown update

[JanProgrammierung]

This pull request includes several changes to the HeaderComponent in the next-app/src/components/HeaderComponent.tsx file to improve performance and code readability. The most important changes include the use of React.memo for memoization, the addition of useCallback for optimizing callback functions, and various updates to class names and JSX elements for better styling and structure.

Performance improvements:

• Wrapped HeaderComponent with React.memo to prevent unnecessary re-renders.
• Added useCallback for toggleMenu and toggleDropdown functions to optimize callback functions.

Code readability and styling updates:

• Replaced div with header for semantic HTML improvement. [1] [2]
• Updated class names in JSX elements for better styling and structure, including the use of clsx for conditional class names. [1] [2]
• Modified the links and dropdownLinks objects to update and reorder the navigation links.