To continue implementing shadcn

[JanProgrammierung]

This pull request includes several updates to the HeaderComponent in the next-app/src/components/HeaderComponent.tsx file to improve performance and code readability. The key changes involve the introduction of useCallback hooks for event handlers, the use of React.memo for component optimization, and the application of clsx for conditional class names.

Performance improvements:

• Added useCallback hooks for toggleMenu and toggleDropdown functions to prevent unnecessary re-renders.

Code readability and optimization:

• Wrapped HeaderComponent with React.memo to memoize the component and prevent re-renders when props do not change.
• Replaced anonymous functions in event handlers with the toggleMenu and toggleDropdown functions. [1] [2]
• Used clsx for conditional class names to simplify the class name logic. [1] [2]

Structural changes:

• Changed the outermost element from a div to a header for semantic HTML purposes. [1] [2]