Let the shell say where home is, and drop the router from the call

The call reached for react-router in five places to send the user
"home": on leaving without a lobby, from the lobby's recents link, from
the post-call screen, from the error page's return button and from the
header logo. Home is the standalone app's home page; the call has no
idea where that is, and a component has no such place at all — its host
decides what follows a call. Yet the component had to mount a
MemoryRouter just so those hooks would not throw.

`useLeaveToHome` is the way home as the shell supplies it: the app
provides `navigate("/")` from inside its router, the component provides
nothing, and everything that used to link to "/" now either calls it or,
when there is none, offers no way out. The logo becomes a plain logo,
the recents and "not now" links disappear, the error page's button does
too. `ClientProvider`'s logout goes the same way. The component no
longer renders a router.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/room/CallView.tsx

@@ -28,7 +28,6 @@ import {
   MatrixRTCSessionEvent,
   type MatrixRTCSession,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { useNavigate } from "react-router-dom";
 
 import { type JoinCallData } from "../widget";
 import { LobbyView } from "./LobbyView";
@@ -72,6 +71,7 @@ import { useBehavior } from "../useBehavior.ts";
 import { useRootElement } from "../RootElementContext.ts";
 import { useHostBridge } from "../HostBridge.ts";
 import { useMuteStates } from "../state/useMuteStates.ts";
+import { useLeaveToHome } from "../LeaveToHomeContext.ts";
 
 /**
  * If there already are this many participants in the call, we automatically mute
@@ -374,7 +374,7 @@ const LoadedCallView: FC<LoadedProps> = ({
   // TODO refactor this + "joined" to just one callState
   const [left, setLeft] = useState(false);
 
-  const navigate = useNavigate();
+  const leaveToHome = useLeaveToHome();
 
   // TODO split this into leave and onDisconnect
   const onLeft = useCallback(
@@ -433,7 +433,7 @@ const LoadedCallView: FC<LoadedProps> = ({
             !confineToRoom &&
             !PosthogAnalytics.instance.isEnabled()
           )
-            void navigate("/");
+            leaveToHome?.();
 
           // After this point the host could dispose of us at any moment!
           try {
@@ -462,7 +462,7 @@ const LoadedCallView: FC<LoadedProps> = ({
       isPasswordlessUser,
       confineToRoom,
       returnToLobby,
-      navigate,
+      leaveToHome,
     ],
   );