Create a single-file WordPress plugin that adds the post featured image (thumbnail) to the admin Posts list table (edit.php?post_type=post) as the FIRST column.
Requirements:
- Hook into manage_posts_columns (and manage_edit-post_columns) to insert a new column key like 'p0_featured_image' at the beginning of the columns array (before the checkbox column ideally, but user asked 1st column; implement as first visible column after checkbox OR as absolute first—prefer absolute first while keeping checkbox functional: keep 'cb' first, then featured image column, then title, etc. Provide filter that inserts right after 'cb' so bulk actions still work and it is effectively first content column.
- Render column content via manage_posts_custom_column / manage_post_posts_custom_column. For each post:
- If has_post_thumbnail: output the thumbnail with get_the_post_thumbnail($post_id, array(50,50), ['style'=>'width:50px;height:50px;object-fit:cover;border-radius:4px;'])
- Else show a placeholder dash or empty gray box with “—”. Use simple HTML with inline style.
- Add minimal CSS in admin_head to constrain column width and align.
- Make the column non-sortable by default (no need for sorting).
- Only apply in wp-admin for post type 'post' main list table, not for pages/CPTs.
- Use proper plugin header, namespaces/prefix functions with p0_pfimg_ prefix, and guard with ABSPATH.
- Security: escape attributes, avoid direct output of unescaped values; use wp_kses_post for thumbnail HTML.
- Performance: do not run on front end; minimal hooks.
- Include small i18n with __() for column header text.
End result: In All Posts admin screen, user sees featured image thumbnails in the first content column.
