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/Abilities/FollowUp.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace LIT\MCP\Abilities;
 
+use LIT\MCP\Log;
 use Throwable;
 
 /**
@@ -20,8 +21,7 @@ final class FollowUp
         try {
             return $step();
         } catch (Throwable $e) {
-            $message = sprintf('[wp-lit-mcp] %s failed: %s', $context, $e);
-            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            Log::failure($context, $e);
             $warnings[] = $warning;
 
             return null;