Add check for spelling “WordPress” correctly

[carolinan]

Closes #131

Checks for wordpress, wordpres, word press.
Skips attributes, block comments, query parameters, etc.

AI usage: this was all written by Copilot.

Testing instructions:
Add the following to an HTML template in a block theme

<!-- wp:social-links -->
<ul class="wp-block-social-links"><!-- wp:social-link {"url":"#hej","service":"wordpress"} /--></ul>
<!-- /wp:social-links -->
 @wordpress
 https://wordpress.org/support/article/404-error-not-found/
 wordpress
 WordPres

Run Theme Check on that theme.
The result should mention the two errors:

REQUIRED: Found incorrect spelling or capitalization of WordPress in the file templates/404.html. Always use WordPress in text.
Line 7: wordpress
Line 8: WordPres