refactor: extract author name extraction logic to a partial

Extracts duplicated logic for resolving an author's name from a generic author object (which can be a map or a string) into a new reusable partial `layouts/partials/get_author_name.html`. Updates multiple files to use this new partial, improving code maintainability.

Co-authored-by: KarelZe <12801659+KarelZe@users.noreply.github.com>