fix: media usage check fails closed on database errors; refused deletes checked for partial state

MediaUsageFinder treats a failed query (null result or last_error) as a possible
usage and an incomplete scan, so media-delete refuses without force. A refused
wp_delete_attachment() is write_failed only when the attachment is intact,
otherwise partial_write. media-update: re-read hint on write_failed, normalized
ids in failures, documented lock resolution and kses on restore.

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

src/Abilities/Errors.php

@@ -102,14 +102,15 @@ final class Errors
      * A write failed and was rolled back completely.
      *
      * @param array<string, mixed> $details Extra error details (e.g. a backup that stays).
+     * @param string|null          $hint    Replaces the default hint (e.g. "re-read before retrying").
      */
-    public static function writeFailed(string $reason, array $details = []): WP_Error
+    public static function writeFailed(string $reason, array $details = [], ?string $hint = null): 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).',
+            $hint ?? 'Eingaben prüfen, ggf. korrigieren und erneut versuchen; tritt der Fehler wieder auf, den '
+                . 'Administrator informieren (Details im PHP-Error-Log der Website).',
             500,
             $details
         );