fix: never publish a missed schedule, refuse trashed posts, fail on meta read errors

- PostGuard::editable() refuses trashed entries unless the caller opts in
  (content-get, revisions-list, post-trash); publish/schedule/unpublish/update/
  restore/duplicate/replace now refuse them.
- PostGuard::statusStable(): content-update, revision-restore and
  replace-with-copy refuse a future post whose date has passed (any save would
  publish it); the content-update rollback and PostCloner row writes re-check.
- PostCloner::ownMeta() treats a failed SELECT as an error; replace() reads the
  copy before its first write.
- replace-with-copy needs create_posts (backup clone) and reports backup_id in
  write_failed/partial_write.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Abilities/Errors.php

@@ -98,15 +98,20 @@ final class Errors
         return self::make('unsupported', $message, $hint, 400);
     }
 
-    /** A write failed and was rolled back completely. */
-    public static function writeFailed(string $reason): WP_Error
+    /**
+     * A write failed and was rolled back completely.
+     *
+     * @param array<string, mixed> $details Extra error details (e.g. a backup that stays).
+     */
+    public static function writeFailed(string $reason, array $details = []): WP_Error
     {
         return self::make(
             'write_failed',
             trim('Speichern fehlgeschlagen: ' . $reason) . ' Nichts wurde gespeichert.',
             'Eingaben prüfen, ggf. korrigieren und erneut versuchen; tritt der Fehler wieder auf, den Administrator '
                 . 'informieren (Details im PHP-Error-Log der Website).',
-            500
+            500,
+            $details
         );
     }