feat: support nlu_skip flag to exclude intermediate flows from NLU catalog

Flows marked with nlu_skip:true are never offered to the NLU router,
preventing the AI from jumping directly to steps that require prior
data collection (e.g. submenu_mantenimiento_fecha needs grupo selected first).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/AiBot.php

@@ -408,6 +408,9 @@ PROMPT;
             if ($isUpload   && !in_array($permType, [1, 3], true)) continue;
             if ($isDownload && !in_array($permType, [2, 3], true)) continue;
 
+            // Flujos marcados como internos — no exponer al NLU
+            if (!empty($flow['nlu_skip'])) continue;
+
             // Skip internal/navigation flows unless they have an explicit NLU description
             $hasNluDesc = isset($flow['nlu_description']) && $flow['nlu_description'] !== '';
             if (in_array($type, ['text', 'image'], true) && !$isUpload && !$isDownload && !$hasNluDesc) continue;