Enhance ImagesViewSet and Images component with site and sector filtering

- Added site_id and sector_id query parameter support in ImagesViewSet for filtering content and task-linked images.
- Implemented event listeners in the Images component to refresh data on site and sector changes.
- Updated image prompt handling to allow undefined values.

frontend/src/pages/Writer/Images.tsx

@@ -153,6 +153,24 @@ export default function Images() {
     loadImages();
   }, [loadImages]);
 
+  // Listen for site and sector changes and refresh data
+  useEffect(() => {
+    const handleSiteChange = () => {
+      loadImages();
+    };
+    
+    const handleSectorChange = () => {
+      loadImages();
+    };
+    
+    window.addEventListener('siteChanged', handleSiteChange);
+    window.addEventListener('sectorChanged', handleSectorChange);
+    return () => {
+      window.removeEventListener('siteChanged', handleSiteChange);
+      window.removeEventListener('sectorChanged', handleSectorChange);
+    };
+  }, [loadImages]);
+
   // Debounced search
   useEffect(() => {
     const timer = setTimeout(() => {
@@ -258,7 +276,7 @@ export default function Images() {
         type: 'in_article',
         position: img.position || idx + 1,
         contentTitle: contentImages.content_title || `Content #${contentId}`,
-        prompt: img.prompt,
+        prompt: img.prompt || undefined,
         status: 'pending',
         progress: 0,
         imageUrl: null,