fix: address confirmed bugs from LOTUS_BUGS.md audit

- useFileDrop: reset drag overlay when mouse leaves browser window
  (relatedTarget === null signals viewport exit, counter was getting stuck)
- useDeviceVerificationStatus: add member count to useMemo deps so new
  room members' devices get checked, not just initial joined members
- index.css: define --bg-surface-variant used by VoiceMessageRecorder,
  MessageSearch, SearchFilters, UserRoomProfile (was falling back to transparent)
- syntaxHighlight: fix Python inline comments — # after space/tab was
  treated as plain text; only start-of-line was recognised
- usePresenceUpdater: replace internal baseUrl cast with mx.getHomeserverUrl()
- useLocalMessageSearch: scan all linked timelines via getUnfilteredTimelineSet()
  not just the live window, so scrolled-back history is included in E2EE search
- RoomViewHeader: show search button in encrypted rooms — local search is
  implemented and handles them; the guard was a holdover from before it existed
- recent-emoji: return emojis in recency order (array is already unshifted on
  use) instead of sorting by total usage count

Skipped: media gallery memory leak (needs virtualization refactor),
bookmark race condition (needs queue/lock), Night Light portal coverage
(position:fixed already covers full viewport — not a real bug).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/hooks/usePresenceUpdater.ts

@@ -77,7 +77,7 @@ export function usePresenceUpdater() {
     const handlePageHide = () => {
       const userId = mx.getUserId();
       const token = mx.getAccessToken();
-      const baseUrl = (mx as unknown as { baseUrl: string }).baseUrl;
+      const baseUrl = mx.getHomeserverUrl();
       if (!userId || !token || !baseUrl) return;
 
       fetch(`${baseUrl}/_matrix/client/v3/presence/${encodeURIComponent(userId)}/status`, {