deps: react-router-dom 4 -> 6 (history 5, react-router-bootstrap 0.26)

Removes the Router/Switch/Route/Link/LinkContainer legacy-context
warnings. Keeps the shared history singleton (used outside React by
NotificationsObserver + Utils/location) via unstable_HistoryRouter, and
bridges v6 hooks back to v4-shaped history/match/location props with a
new withRouterCompat HOC so the ~20 class pages stay untouched.

- <Switch> -> <Routes>, component= -> element=
- Authenticated/Public -> guard components (children or <Navigate replace>)
- LocationListener -> useLocation + useEffect function
- regex route /fire/:type(active|archive|alert)/:id -> /fire/:type/:id
- history.listen callback is ({ location }) in history v5

Browser-verified: SPA nav, /subscriptions->/login auth redirect,
deep-link /fire/archive/:id (params), browser back/forward. REST smoke
byte-identical.

imports/ui/components/Public/Public.js

@@ -1,27 +1,20 @@
 import React from 'react';
 import PropTypes from 'prop-types';
-import { Route, Redirect } from 'react-router-dom';
+import { Navigate, useLocation } from 'react-router-dom';
 
-const Public = ({
-  loggingIn, authenticated, component, location, path, exact, ...rest
-}) => (
-  <Route
-    path={path}
-    exact={exact}
-    render={props => (
-      !authenticated ?
-      (React.createElement(component, {
- ...props, ...rest, loggingIn, authenticated
-})) :
-      (<Redirect to={{ pathname: '/subscriptions', state: location.state }} />)
-    )}
-  />
-);
+// v6 route guard for public-only pages (login/signup/auth): rendered as a route
+// `element` wrapping the real page. Redirects authenticated users to their
+// subscriptions, preserving any location state (e.g. a pending new-zone flow).
+const Public = ({ authenticated, children }) => {
+  const location = useLocation();
+  return authenticated
+    ? <Navigate to="/subscriptions" state={location.state} replace />
+    : children;
+};
 
 Public.propTypes = {
-  loggingIn: PropTypes.bool.isRequired,
   authenticated: PropTypes.bool.isRequired,
-  component: PropTypes.elementType.isRequired
+  children: PropTypes.node.isRequired
 };
 
 export default Public;