feat: scaffold codespace backend

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/response/response.go

@@ -0,0 +1,29 @@
+package response
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+type ErrorBody struct {
+	Error ErrorDetail `json:"error"`
+}
+
+type ErrorDetail struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+}
+
+func JSON(w http.ResponseWriter, status int, value any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(value)
+}
+
+func Error(w http.ResponseWriter, status int, code string, err error) {
+	msg := code
+	if err != nil {
+		msg = err.Error()
+	}
+	JSON(w, status, ErrorBody{Error: ErrorDetail{Code: code, Message: msg}})
+}