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/Server/ServerRegistrar.php

@@ -7,6 +7,7 @@ namespace LIT\MCP\Server;
 use LIT\MCP\Abilities\ExposurePolicy;
 use LIT\MCP\Guides\InstructionsBuilder;
 use LIT\MCP\Integrations\IntegrationRegistry;
+use LIT\MCP\Log;
 use LIT\MCP\Plugin;
 use WP\MCP\Core\McpAdapter;
 use WP\MCP\Infrastructure\ErrorHandling\ErrorLogMcpErrorHandler;
@@ -131,8 +132,7 @@ final class ServerRegistrar
         $result = ($this->createAdapterServer)($args);
 
         if (is_wp_error($result)) {
-            $message = '[wp-lit-mcp] MCP server registration failed: ' . $result->get_error_message();
-            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            Log::failure('MCP server registration', $result->get_error_message());
         }
     }