Fix TypeScript error: Add ai_image property to Slide interface

- Added ai_image?: string to Slide interface to match backend response
- Fixed downloads.ts to use ai_image instead of non-existent visual_url
- This resolves the production build TypeScript error

lib/downloads.ts

@@ -108,12 +108,12 @@ export const downloadAllSlides = async (
 ) => {
   for (let i = 0; i < slides.length; i++) {
     const slide = slides[i];
-    if (slide.visual_url) {
+    if (slide.ai_image) {
       // Add delay between downloads to avoid browser blocking
       if (i > 0) {
         await new Promise(resolve => setTimeout(resolve, 200));
       }
-      downloadSlideImage(slide.visual_url, slide.title, slide.id, documentId);
+      downloadSlideImage(slide.ai_image, slide.title, slide.id, documentId);
     }
   }
 };

types/index.ts

@@ -21,6 +21,7 @@ export interface Slide {
   type: 'title' | 'content' | 'chart' | 'stats';
   visual_type?: 'none' | 'bar_chart' | 'pie_chart' | 'stats_grid' | 'icon_grid';
   visual_data?: any;
+  ai_image?: string;
 }
 
 export interface DebatePoint {