feat: respond with json

internal/auth/routes.go

@@ -132,6 +132,8 @@ func (h *AuthHandler) login(w http.ResponseWriter, r *http.Request) {
 		// Avatar
 	}
 
+	w.Header().Set("Content-Type", "application/json")
+
 	if err := encoder.Encode(Response{
 		AccessToken:    accessToken,
 		RefreshToken:   refreshToken,