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/Utils/location.js

@@ -7,9 +7,9 @@ import history from '/imports/ui/components/History/History';
 export const location = new ReactiveVar(history.location.pathname);
 
 if (Meteor.isClient) {
-  history.listen((loc) => { // , action) => {
-    // console.log(`The current URL is ${location.pathname}${location.search}${location.hash}`)
-    // console.log(`The last navigation action was ${action}`)
+  // history v5 hands the listener a { location, action } update object
+  // (v4 passed the location directly).
+  history.listen(({ location: loc }) => {
     location.set(loc.pathname);
   });
 }