refactor: extract various constants

frontend/src/ui/BreadcrumbTrail.tsx

@@ -8,6 +8,12 @@ import React, {
 import { createPortal } from 'react-dom';
 import PropTypes from 'prop-types';
 import useFloatingMenu from './useFloatingMenu';
+import {
+  ELLIPSIS,
+  WIDTH_BUFFER_RATIO,
+  WIDTH_CHANGE_TOLERANCE,
+  WIDTH_TOLERANCE,
+} from '../constants/ui';
 
 const normalizeEntries = (entries) =>
   (Array.isArray(entries) ? entries : [])
@@ -22,11 +28,6 @@ const normalizeEntries = (entries) =>
     })
     .filter(Boolean);
 
-const ELLIPSIS = { id: '__breadcrumbs_ellipsis__', label: '…', onClick: null, raw: null };
-const WIDTH_TOLERANCE = 1;
-const WIDTH_BUFFER_RATIO = 0.95;
-const WIDTH_CHANGE_TOLERANCE = 0.25;
-
 const BreadcrumbTrail = ({
   entries = [],
   className = '',