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/Log.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP;
+
+use Throwable;
+
+/**
+ * The plugin's one way into the PHP error log. Messages carry the "[wp-lit-mcp]" prefix; the
+ * log is for the site operator only and may contain details (paths, traces) that must never
+ * reach an MCP client.
+ */
+final class Log
+{
+    private const PREFIX = '[wp-lit-mcp] ';
+
+    /** Logs "[wp-lit-mcp] <context> failed: <detail>"; a Throwable is logged with its trace. */
+    public static function failure(string $context, Throwable|string $detail): void
+    {
+        self::line(sprintf('%s failed: %s', $context, (string) $detail));
+    }
+
+    /** Logs one free-form line with the plugin prefix. */
+    public static function line(string $message): void
+    {
+        error_log(self::PREFIX . $message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+    }
+}