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/pages/page-submit.php

@@ -26,13 +26,6 @@ if (empty($ctx['enabled'])) {
 	return;
 }
 
-// Guest without guest mode → login.
-if (!empty($ctx['is_guest']) && empty($ctx['settings']['guest_enabled'])) {
-	$login = function_exists('aksrt_get_login_url') ? aksrt_get_login_url(get_permalink()) : wp_login_url(get_permalink());
-	wp_safe_redirect($login);
-	exit;
-}
-
 // Invalid edit id → strip.
 if (!empty($_GET['edit']) && empty($ctx['edit_post'])) {
 	wp_safe_redirect(remove_query_arg('edit'));
@@ -103,7 +96,6 @@ if (file_exists($js)) {
 			],
 
 
-		'leaveWarning' => !empty($ctx['settings']['leave_warning']),
 		'imageUploadMultiple' => $image_upload_multiple,
 		'ai'        => [
 			'available' => !empty($ctx['ai_available']),