refactor: PostRow::update and PostGuard::assertNoMissedSchedule (M5)

- PostRow::update(id, columns, failure) / ::save(): the slashed wp_update_post of
  internal row writes, refusals as RuntimeException '<failure>: <why>'. Used by
  ContentUpdate::restoreRow, PostCloner::updateRow, MediaMetaWriter apply/restore.
- PostGuard::assertNoMissedSchedule(postId, message) replaces the re-read + check in
  ContentUpdate::restoreRow, PostCloner and DiviSaver::restore (DiviSaver keeps its
  own kses window; M4).
- PostCloner::restore uses Rollback::attempt.
Log messages unchanged.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Media/MediaMetaWriter.php

@@ -4,8 +4,8 @@ declare(strict_types=1);
 
 namespace LIT\MCP\Integrations\Media;
 
+use LIT\MCP\Integrations\WordPress\PostRow;
 use RuntimeException;
-use WP_Error;
 use WP_Post;
 
 /**
@@ -58,15 +58,11 @@ final class MediaMetaWriter
         if ($columns !== []) {
             // Set before the call: a throwing save_post hook runs after the row was written.
             $touched = true;
-            $result = wp_update_post(wp_slash(array_merge($columns, ['ID' => $id])), true);
-            if ($result instanceof WP_Error || ! $result) {
+            $refusal = PostRow::save($id, $columns);
+            if ($refusal !== null) {
                 // wp_update_post() reports errors before it writes anything.
                 $touched = false;
-                throw new RuntimeException(sprintf(
-                    'Attachment %d not updated: %s',
-                    $id,
-                    $result instanceof WP_Error ? $result->get_error_message() : 'unknown error'
-                ));
+                throw new RuntimeException(sprintf('Attachment %d not updated: %s', $id, $refusal));
             }
         }
 
@@ -84,14 +80,7 @@ final class MediaMetaWriter
     {
         $id = $snapshot['id'];
         if ($snapshot['columns'] !== []) {
-            $result = wp_update_post(wp_slash(array_merge($snapshot['columns'], ['ID' => $id])), true);
-            if ($result instanceof WP_Error || ! $result) {
-                throw new RuntimeException(sprintf(
-                    'Attachment %d not restored: %s',
-                    $id,
-                    $result instanceof WP_Error ? $result->get_error_message() : 'unknown error'
-                ));
-            }
+            PostRow::update($id, $snapshot['columns'], sprintf('Attachment %d not restored', $id));
         }
 
         if (! $snapshot['alt_changed']) {