fix: set content-type to json

internal/user/routes.go

@@ -98,6 +98,8 @@ func (h *UserHandler) register(w http.ResponseWriter, r *http.Request) {
 		Id string `json:"id"`
 	}
 
+	w.Header().Set("Content-Type", "application/json")
+
 	if err := encoder.Encode(Response{
 		Id: id.String(),
 	}); err != nil {
@@ -184,6 +186,8 @@ func (h *UserHandler) uploadAvatar(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(http.StatusOK)
 	encoder := json.NewEncoder(w)
 
+	w.Header().Set("Content-Type", "application/json")
+
 	if err := encoder.Encode(Response{AvatarID: uploadInfo.Key}); err != nil {
 		web.Error(w, "failed to write response", http.StatusInternalServerError)
 	}