feat(serialization): implement Gin JSON/YAML binding

- Introduce SubstituteEnvReader that replaces ${VAR} patterns with environment variable
  values, properly quoted for JSON/YAML compatibility
- Gin bindings (JSON/YAML) that use the environment-substituting reader
  for request body binding with validation support

internal/serialization/gin_binding.go

@@ -0,0 +1,37 @@
+package serialization
+
+import (
+	"net/http"
+
+	"github.com/bytedance/sonic"
+	"github.com/goccy/go-yaml"
+)
+
+type (
+	GinJSONBinding struct{}
+	GinYAMLBinding struct{}
+)
+
+func (b GinJSONBinding) Name() string {
+	return "json"
+}
+
+func (b GinJSONBinding) Bind(req *http.Request, obj any) error {
+	m := make(map[string]any)
+	if err := sonic.ConfigDefault.NewDecoder(NewSubstituteEnvReader(req.Body)).Decode(&m); err != nil {
+		return err
+	}
+	return MapUnmarshalValidate(m, obj)
+}
+
+func (b GinYAMLBinding) Name() string {
+	return "yaml"
+}
+
+func (b GinYAMLBinding) Bind(req *http.Request, obj any) error {
+	m := make(map[string]any)
+	if err := yaml.NewDecoder(NewSubstituteEnvReader(req.Body)).Decode(&m); err != nil {
+		return err
+	}
+	return MapUnmarshalValidate(m, obj)
+}