Stop asking whether Element Call is a widget

The remaining reads of the widget global were all asking one of two
different questions, so they get two different answers.

The app shell — the auth hooks, automatic guest registration, the group
call loader's diagnostic and the initial mute state — wants to know
whether Element Call was launched as a widget. That is a property of the
URL it was launched with, so expose the isWidget that computeUrlParams
already computed internally, documented as being for shell use only.

The call interface — whether to offer the profile settings tab — wants to
know something about its host, so it asks the bridge. A host that can
dismiss Element Call owns the user's account, so their profile is not ours
to edit; this reuses the close capability as a proxy, with a TODO
alongside the others.

ClientContext also takes supportsReactions from the bridge rather than
checking four widget capabilities itself, which removes widgetApi from
InitResult — a field that was always null outside widget mode.

Note this changes behaviour for a malformed widget URL: one carrying a
widget ID and parent URL but missing the room, user, device or base URL
would previously have fallen back to registering a guest user, and will
now not.

src/settings/SettingsModal.tsx

@@ -18,7 +18,7 @@ import { ProfileSettingsTab } from "./ProfileSettingsTab";
 import { FeedbackSettingsTab } from "./FeedbackSettingsTab";
 import { iosDeviceMenu$ } from "../state/MediaDevices";
 import { useMediaDevices } from "../MediaDevicesContext";
-import { widget } from "../widget";
+import { useHostBridge } from "../HostBridge";
 import {
   useSetting,
   soundEffectVolume as soundEffectVolumeSetting,
@@ -123,6 +123,7 @@ export const SettingsModal: FC<Props> = ({
   // On EC, we decided that it is less confusing for the user if they see those options in the output section
   // rather than the input section.
   const { controlledAudioDevices } = useUrlParams();
+  const hostBridge = useHostBridge();
   // If we are on iOS we will show a button to open the native audio device picker.
   const iosDeviceMenu = useBehavior(iosDeviceMenu$);
 
@@ -234,7 +235,9 @@ export const SettingsModal: FC<Props> = ({
   };
 
   const tabs = [audioTab, videoTab];
-  if (widget === null) tabs.push(profileTab);
+  // A host that can dismiss us is a host that owns the user's account, so their
+  // profile is not ours to edit.
+  if (hostBridge.close === undefined) tabs.push(profileTab);
   tabs.push(preferencesTab);
   if (isRageshakeAvailable || import.meta.env.VITE_PACKAGE === "full") {
     // for full package we want to show the analytics consent checkbox