feat(photos): add square medium variant for sharp grid thumbnails

backend/internal/photos/pipeline.go

@@ -121,24 +121,31 @@ func ExtractEXIFAttributes(data []byte) map[string]any {
 	return extractEXIF(data).Attributes
 }
 
-func buildVariants(data []byte) (thumb, preview []byte, err error) {
+func buildVariants(data []byte) (thumb, medium, preview []byte, err error) {
 	img, err := imaging.Decode(bytes.NewReader(data), imaging.AutoOrientation(true))
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
-	thumbImg := imaging.Fit(img, 200, 200, imaging.Lanczos)
+	// Grid variants are square crops so a square tile is never upscaled; the
+	// viewer preview keeps the aspect ratio.
+	thumbImg := imaging.Fill(img, 200, 200, imaging.Center, imaging.Lanczos)
+	mediumImg := imaging.Fill(img, 800, 800, imaging.Center, imaging.Lanczos)
 	previewImg := imaging.Fit(img, 1200, 1200, imaging.Lanczos)
 
 	opts := webp.Options{Quality: 82}
 	var thumbBuf bytes.Buffer
 	if err := webp.Encode(&thumbBuf, thumbImg, opts); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
+	}
+	var mediumBuf bytes.Buffer
+	if err := webp.Encode(&mediumBuf, mediumImg, opts); err != nil {
+		return nil, nil, nil, err
 	}
 	var previewBuf bytes.Buffer
 	if err := webp.Encode(&previewBuf, previewImg, opts); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
-	return thumbBuf.Bytes(), previewBuf.Bytes(), nil
+	return thumbBuf.Bytes(), mediumBuf.Bytes(), previewBuf.Bytes(), nil
 }
 
 // checksum returns the hex-encoded SHA-256 of the given bytes.