fix: resolve all golangci-lint errors

- Add blank lines before return statements (nlreturn)
- Remove unused metaCacheMu field and sync import (unused)
- Rename unused groups parameter to _ (revive)
- Use StorageFilePerm constant instead of magic 0600 (mnd, gosec)
- Add nolint directive for vipsOnce global (gochecknoglobals)

internal/imgcache/processor.go

@@ -12,7 +12,7 @@ import (
 )
 
 // vipsOnce ensures vips is initialized exactly once.
-var vipsOnce sync.Once
+var vipsOnce sync.Once //nolint:gochecknoglobals // package-level sync.Once for one-time vips init
 
 // initVips initializes libvips with quiet logging.
 func initVips() {
@@ -38,6 +38,7 @@ type ImageProcessor struct{}
 // NewImageProcessor creates a new image processor.
 func NewImageProcessor() *ImageProcessor {
 	initVips()
+
 	return &ImageProcessor{}
 }
 
@@ -177,6 +178,7 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 		scale := min(scaleW, scaleH)
 		newW := int(float64(imgW) * scale)
 		newH := int(float64(imgH) * scale)
+
 		return img.Thumbnail(newW, newH, vips.InterestingNone)
 
 	case FitFill:
@@ -194,6 +196,7 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 		scale := min(scaleW, scaleH)
 		newW := int(float64(imgW) * scale)
 		newH := int(float64(imgH) * scale)
+
 		return img.Thumbnail(newW, newH, vips.InterestingNone)
 
 	case FitOutside:
@@ -204,6 +207,7 @@ func (p *ImageProcessor) resize(img *vips.ImageRef, width, height int, fit FitMo
 		scale := max(scaleW, scaleH)
 		newW := int(float64(imgW) * scale)
 		newH := int(float64(imgH) * scale)
+
 		return img.Thumbnail(newW, newH, vips.InterestingNone)
 
 	default: