Phase A: clear all react-hooks/exhaustive-deps warnings via useEffectEvent or hoisting

Eliminate the four remaining missing-dependency warnings reported by
react-hooks v7. Each one was a real stale-closure or re-trigger hazard;
the fix matches the intent rather than just silencing the linter.

- src/App.tsx (line 448): wrap showSessionExpired with useEffectEvent
  (onSessionExpired) so the prepare effect doesn't re-run on every
  showSessionExpired identity change but still calls the latest
  callback. Replace the two in-effect call sites.
- src/components/furni-editor/views/FurniEditorSearchView.tsx: wrap
  the on-mount onSearch('', '', 1) call with useEffectEvent so the
  callback prop isn't a missing dependency.
- src/components/notification-center/views/bubble-layouts/
  NotificationBadgeReceivedBubbleView.tsx: wrap the
  "fetch badges only if empty on mount" check with useEffectEvent
  so badgeCodes.length isn't required as a dep (and won't re-fetch
  every count change).
- src/components/navigator/views/room-settings/
  NavigatorRoomSettingsRightsTabView.tsx: switch deps from
  roomData?.roomId to roomData (the body uses roomData.roomId after
  an early return; the linter wanted the whole object).
- src/api/ui-settings/UiSettingsContext.tsx: hoist ALL_CSS_VARS
  outside the component (it's a static constant).

After this, yarn eslint reports zero exhaustive-deps warnings across
the whole src/.

https://claude.ai/code/session_01GrR87LAqnAEyKG2ZbmQt5Q

src/api/ui-settings/UiSettingsContext.tsx

@@ -60,6 +60,13 @@ const saveSettings = (settings: IUiSettings): void =>
     {}
 };
 
+const ALL_CSS_VARS = [
+    '--ui-accent-color', '--ui-accent-dark',
+    '--ui-ctx-bg', '--ui-ctx-header-bg', '--ui-ctx-item-bg1', '--ui-ctx-item-bg2',
+    '--ui-btn-primary-bg', '--ui-btn-primary-border',
+    '--ui-dark-bg', '--ui-dark-border'
+];
+
 const sendComposer = (composer: any): void =>
 {
     try
@@ -189,13 +196,6 @@ export const UiSettingsProvider: FC<PropsWithChildren> = ({ children }) =>
 
     const isCustomActive = settings.colorMode !== 'default';
 
-    const ALL_CSS_VARS = [
-        '--ui-accent-color', '--ui-accent-dark',
-        '--ui-ctx-bg', '--ui-ctx-header-bg', '--ui-ctx-item-bg1', '--ui-ctx-item-bg2',
-        '--ui-btn-primary-bg', '--ui-btn-primary-border',
-        '--ui-dark-bg', '--ui-dark-border'
-    ];
-
     useEffect(() =>
     {
         const root = document.documentElement;