refactor: one logging helper LIT\MCP\Log (M6)

Log::failure(context, detail) keeps the '[wp-lit-mcp] <context> failed: <detail>'
format of the nine former error_log() sites; Log::line() covers the change log line.
One phpcs ignore instead of eleven.

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

src/Integrations/Media/MediaImporter.php

@@ -7,6 +7,7 @@ namespace LIT\MCP\Integrations\Media;
 use LIT\MCP\Abilities\Errors;
 use LIT\MCP\Abilities\WriteFailed;
 use LIT\MCP\Limits;
+use LIT\MCP\Log;
 use Throwable;
 use WP_Error;
 
@@ -197,8 +198,7 @@ class MediaImporter
         );
         if ($attachmentId instanceof WP_Error) {
             // WordPress' message can contain server paths: only for the log, not for the client.
-            $message = sprintf('[wp-lit-mcp] media sideload failed: %s', $attachmentId->get_error_message());
-            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            Log::failure('media sideload', $attachmentId->get_error_message());
 
             return Errors::writeFailed(
                 'WordPress hat die Datei nicht übernommen (z. B. Upload-Verzeichnis nicht beschreibbar).'

src/Integrations/Media/MediaUsageFinder.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace LIT\MCP\Integrations\Media;
 
 use Closure;
+use LIT\MCP\Log;
 
 /**
  * Finds where an attachment is used (spec §6.3). Deliberately errs on the side of "used":
@@ -165,8 +166,7 @@ class MediaUsageFinder
         }
 
         $this->queryFailed = true;
-        $message = sprintf('[wp-lit-mcp] media usage query failed: %s', (string) $wpdb->last_error);
-        error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+        Log::failure('media usage query', (string) $wpdb->last_error);
 
         return [];
     }