Implement AVIF decoding support

- Add github.com/gen2brain/avif dependency (CGO-free, WASM-based)
- Update decode() to try AVIF after WebP
- Add AVIF to SupportedInputFormats()

internal/imgcache/processor.go

@@ -12,6 +12,7 @@ import (
 	"io"
 
 	"github.com/disintegration/imaging"
+	goavif "github.com/gen2brain/avif"
 	gowebp "github.com/gen2brain/webp"
 	"golang.org/x/image/webp"
 )
@@ -121,6 +122,7 @@ func (p *ImageProcessor) SupportedInputFormats() []string {
 		string(MIMETypePNG),
 		string(MIMETypeGIF),
 		string(MIMETypeWebP),
+		string(MIMETypeAVIF),
 	}
 }
 
@@ -152,6 +154,14 @@ func (p *ImageProcessor) decode(data []byte) (image.Image, string, error) {
 		return img, "webp", nil
 	}
 
+	// Try AVIF
+	r.Reset(data)
+
+	img, err = goavif.Decode(r)
+	if err == nil {
+		return img, "avif", nil
+	}
+
 	return nil, "", fmt.Errorf("unsupported image format")
 }