feat: ability and integration infrastructure

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

src/Abilities/Errors.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use WP_Error;
+
+/**
+ * Factory for the error objects abilities return. The MCP adapter turns them
+ * into tool results with isError: true.
+ */
+final class Errors
+{
+    public static function forbidden(string $message): WP_Error
+    {
+        return new WP_Error('lit_forbidden', $message, ['status' => 403]);
+    }
+
+    /** @param array<string, string> $fields */
+    public static function invalidInput(string $message, array $fields = []): WP_Error
+    {
+        return new WP_Error('lit_validation_failed', $message, ['status' => 400, 'fields' => $fields]);
+    }
+
+    public static function notFound(string $message): WP_Error
+    {
+        return new WP_Error('lit_not_found', $message, ['status' => 404]);
+    }
+
+    public static function internal(): WP_Error
+    {
+        return new WP_Error(
+            'lit_internal_error',
+            'Interner Fehler bei der Ausführung. Details stehen im PHP-Error-Log der Website.',
+            ['status' => 500]
+        );
+    }
+}