feat: description file for custom theme; use gjson (#433)

* feat: description file for custom theme; use gjson

* fix gosec

* remove outdated stuff

pkg/utils/hfs.go

@@ -0,0 +1,33 @@
+package utils
+
+import (
+	"embed"
+	"io/fs"
+	"os"
+)
+
+// HybridFS combines embed.FS and os.DirFS.
+type HybridFS struct {
+	embedFS, dir fs.FS
+}
+
+func NewHybridFS(embed embed.FS, subDir string, localDir string) (*HybridFS, error) {
+	subFS, err := fs.Sub(embed, subDir)
+	if err != nil {
+		return nil, err
+	}
+
+	return &HybridFS{
+		embedFS: subFS,
+		dir:     os.DirFS(localDir),
+	}, nil
+}
+
+func (hfs *HybridFS) Open(name string) (fs.File, error) {
+	// Ensure embed files are not replaced
+	if file, err := hfs.embedFS.Open(name); err == nil {
+		return file, nil
+	}
+
+	return hfs.dir.Open(name)
+}