Add backend foundation and config-driven workbench

backend/internal/httpx/httpx.go

@@ -0,0 +1,39 @@
+package httpx
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"cmr-backend/internal/apperr"
+)
+
+func WriteJSON(w http.ResponseWriter, status int, payload any) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(payload)
+}
+
+func WriteError(w http.ResponseWriter, err error) {
+	if appErr := apperr.From(err); appErr != nil {
+		WriteJSON(w, appErr.Status, map[string]any{
+			"error": map[string]any{
+				"code":    appErr.Code,
+				"message": appErr.Message,
+			},
+		})
+		return
+	}
+
+	WriteJSON(w, http.StatusInternalServerError, map[string]any{
+		"error": map[string]any{
+			"code":    "internal_error",
+			"message": "internal server error",
+		},
+	})
+}
+
+func DecodeJSON(r *http.Request, dst any) error {
+	decoder := json.NewDecoder(r.Body)
+	decoder.DisallowUnknownFields()
+	return decoder.Decode(dst)
+}