refactor: update UI layout for buttons and add forms documentation

This commit refactors the `ButtonsScreen` to improve responsiveness and layout consistency, and introduces initial documentation for form components in the `FormsScreen`.

### Key Changes:

*   **Buttons Screen Refactor (`buttons_screen.dart`):**
    *   Replaced `Row` and `Gap` combinations in button examples with `Wrap` widgets to allow for better wrapping on smaller screens.
    *   Simplified the layout hierarchy by removing redundant `Row` and `ConstrainedBox` wrappers around `CodeCard` components.
    *   Adjusted the maximum width of the main content container to `752` for better readability.
    *   Standardized padding and alignment for section headers and descriptions.

*   **Forms Screen Enhancements (`forms_screen.dart`):**
    *   Added a new section for "Text-Eingaben" (Text Inputs) showcasing the use of `FormField` with `TextField`.
    *   Included a code example demonstrating how to implement a `TextFieldKey`, `LengthValidator`, and `placeholder` text within a constrained `SizedBox`.
    *   Improved the layout structure of the forms documentation to match the buttons screen.

Author: vmeng-b