Starterkit.php class name casing breaks theme generation on Linux

Problem/Motivation

Drupal GenerateTheme command looks for Drupal\prototype\StarterKit with capital K, but the file is named Starterkit.php with lowercase k. On Linux's case-sensitive filesystem (including inside DDEV), PSR-4 autoloading silently skips postProcess(), leaving the tests/ directory in the generated theme. Template discovery then picks up test templates over the real bridge templates, breaking paragraph rendering.

Steps to reproduce

1. Run the generator from the prototype directory — generator.php uses relative chdir calls and must be run with CWD set to the prototype theme folder:

ddev exec sh -c "cd web/themes/contrib/prototype && php generator.php -n my_theme -d 'My Theme' -p themes/custom"

2. Inspect web/themes/custom/my_theme/ — the tests/ directory is present.
3. Enable the theme, add a Slideshow paragraph to a node — the test template renders instead of the real bridge template.

Proposed resolution

Rename `src/Starterkit.php` to `src/StarterKit.php`, updates the class declaration, and corrects the `.starterkit.yml` ignore patterns.