fix(admin): replicate reference front-submit settings page 1:1

- Rewrite post_list/submit schema (PHP + JS) with the reference theme's
  field set, order, defaults and dependencies; topics fields excluded
- Map PostDisplay::get_submit_settings() and the FrontSubmit runtime to
  the new keys without legacy fallback
- Guest submission follows the capability matrix; category required on
  submit; pay limits read from the cash/points fieldset
- Drop dead front_submit_* settings, template branches and JS config
- Add submit settings reference contract test

templates/parts/submit/featured.php

@@ -7,9 +7,6 @@
  */
 defined('ABSPATH') || exit;
 
-if (empty($ctx['settings']['allow_cover'])) {
-	return;
-}
 if (empty($ctx['can_cover_image']) && empty($ctx['can_cover_slide']) && empty($ctx['can_cover_video'])) {
 	return;
 }