Fix: thumbnail rendering aspect ratios and spreadsheet layouts

backend/workers/thumbnails.go

@@ -161,6 +161,18 @@ func generateOfficeThumbnail(filePath, destPath string, cfg *config.Config) erro
 		"outputtype": "jpg",
 		"title":      "preview.jpg",
 		"url":        fileUrl,
+		"thumbnail": map[string]interface{}{
+			"aspect": 0,
+			"first":  true,
+			"width":  1024,
+			"height": 1024,
+		},
+		"spreadsheetLayout": map[string]interface{}{
+			"ignorePrintArea": true,
+			"printGridlines":  true,
+			"printHeadings":   true,
+			"fitToWidth":      1,
+		},
 	}
 
 	payloadBytes, err := json.Marshal(payload)

frontend/src/components/ThumbnailImage.tsx

@@ -18,7 +18,7 @@ export default function ThumbnailImage({ checksum, fallbackIcon, downloadToken }
         key={key}
         src={downloadToken ? `${api.getThumbnailUrl(checksum, downloadToken)}${errorCount > 0 ? `&t=${key}` : ''}` : ''}
         alt=""
-        className="w-full h-full object-cover"
+        className="w-full h-full object-contain"
         style={{ display: showFallback ? 'none' : 'block' }}
         onError={(e) => {
           if (errorCount < 5) {