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/ChangeLog/ChangeLog.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace LIT\MCP\ChangeLog;
 
 use LIT\MCP\Abilities\FollowUp;
+use LIT\MCP\Log;
 use LIT\MCP\Server\RequestContext;
 
 /**
@@ -57,8 +58,7 @@ class ChangeLog
         );
 
         if ($inserted === false) {
-            $message = sprintf('[wp-lit-mcp] change log insert failed for %s %s:%s', $ability, $objectType, $objectId);
-            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            Log::line(sprintf('change log insert failed for %s %s:%s', $ability, $objectType, $objectId));
             return null;
         }