feat: media via AI, text via NormalBot only, ai_for_media toggle

- Text/interactive/button messages → NormalBot only, never escalates to AI
- Image/audio/video/document → AiBot.processMedia() if ai_for_media enabled,
  else falls back to category greeting menu
- AiBot.processMedia() uses permission_type context so AI acknowledges uploads
  for perm 3 and redirects others to their menu
- WpWebhook.handleMedia now calls BotRouter so the bot responds to media
- Admin UI: checkbox toggle "Procesar imágenes y archivos con IA" in AI tab
- categoryMenuFallback() extracted in BotRouter as shared helper

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

public/index.php

@@ -409,6 +409,7 @@ $routes = [
         if ($aiTemp !== '') $config['ai_temperature'] = (float)$aiTemp;
         $aiProvider = trim($_POST['ai_provider'] ?? '');
         if ($aiProvider !== '') $config['ai_provider'] = $aiProvider;
+        $config['ai_for_media'] = isset($_POST['ai_for_media']);
 
         // Per-category menus
         $perTypeMenus = $_POST['per_type_menu'] ?? [];