Add detailed logging for image conversions on cache miss

Log includes:
- file path
- input/output format
- input/output size in bytes
- input/output dimensions
- size ratio (percentage)

Also adds InputWidth, InputHeight, InputFormat to ProcessResult

internal/imgcache/service.go

@@ -162,6 +162,22 @@ func (s *Service) fetchAndProcess(ctx context.Context, req *ImageRequest) (*Imag
 		return nil, fmt.Errorf("image processing failed: %w", err)
 	}
 
+	// Log conversion details
+	inputSize := int64(len(sourceData))
+	outputSize := processResult.ContentLength
+	sizePercent := float64(outputSize) / float64(inputSize) * 100.0 //nolint:mnd // percentage calculation
+
+	s.log.Info("image converted",
+		"file", req.SourcePath,
+		"input_format", processResult.InputFormat,
+		"output_format", req.Format,
+		"input_bytes", inputSize,
+		"output_bytes", outputSize,
+		"input_dimensions", fmt.Sprintf("%dx%d", processResult.InputWidth, processResult.InputHeight),
+		"output_dimensions", fmt.Sprintf("%dx%d", processResult.Width, processResult.Height),
+		"size_ratio", fmt.Sprintf("%.1f%%", sizePercent),
+	)
+
 	// Store output content to cache
 	metaID, err := s.cache.GetSourceMetadataID(ctx, req)
 	if err != nil {