feat: structured errors with hint, ToolResult, cursor pagination

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Abilities/JsonMap.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use stdClass;
+
+/**
+ * PHP encodes an empty array as JSON [] – for schema type "object" the client
+ * must see {}. WordPress' output validation accepts stdClass for objects.
+ */
+final class JsonMap
+{
+    /**
+     * @param array<string, mixed> $map
+     * @return array<string, mixed>|stdClass
+     */
+    public static function of(array $map): array|stdClass
+    {
+        return $map === [] ? new stdClass() : $map;
+    }
+}