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/imgcache.go

@@ -187,6 +187,12 @@ type ProcessResult struct {
 	Width int
 	// Height is the output image height
 	Height int
+	// InputWidth is the original image width before processing
+	InputWidth int
+	// InputHeight is the original image height before processing
+	InputHeight int
+	// InputFormat is the detected input format (e.g., "jpeg", "png")
+	InputFormat string
 }
 
 // Storage handles persistent storage of cached content

internal/imgcache/processor.go

@@ -93,6 +93,9 @@ func (p *ImageProcessor) Process(
 		ContentType:   ImageFormatToMIME(outputFormat),
 		Width:         finalBounds.Dx(),
 		Height:        finalBounds.Dy(),
+		InputWidth:    origWidth,
+		InputHeight:   origHeight,
+		InputFormat:   format,
 	}, nil
 }
 

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 {