Add proxy endpoint to fix CORS issues for file previews

- Create new `/api/files/proxy-preview` endpoint that fetches and serves files directly
- Update FilePreviewModal to use proxy endpoint for images and PDFs
- Set appropriate headers for inline display and caching
- Remove trailing slash from folder display names in file list

components/FilePreviewModal.vue

@@ -155,13 +155,16 @@ const loadPreview = async () => {
   previewUrl.value = '';
   
   try {
-    const response = await $fetch('/api/files/preview', {
-      params: { fileName: props.file.name },
-    });
-    
-    previewUrl.value = response.url;
+    // For images and PDFs, use the proxy endpoint to avoid CORS issues
+    if (isImage.value || isPdf.value) {
+      // Use the proxy endpoint that serves the file directly
+      previewUrl.value = `/api/files/proxy-preview?fileName=${encodeURIComponent(props.file.name)}`;
+      // The loading state will be handled by the image/iframe onload event
+    } else {
+      throw new Error('File type does not support preview');
+    }
   } catch (err: any) {
-    error.value = err.data?.statusMessage || 'Failed to load preview';
+    error.value = err.data?.statusMessage || err.message || 'Failed to load preview';
     loading.value = false;
   }
 };