Bug fixes, security hardening, and performance improvements

- BUG-16: Fixed pagination deadlock (fetching flag stuck on error path)
- BUG-17: Fixed absoluteIndex===0 falsy check skipping unread jump
- BUG-19: Fixed mEvt.getRoomId()! non-null assertion crash
- BUG-20: Wrapped getSettings()/setSettings() in try/catch for corrupt localStorage
- SEC: Replaced randomStr() Math.random() with crypto.getRandomValues() CSPRNG
- SEC: Fixed afterLoginRedirectPath open redirect validation
- SEC: Narrowed OSM iframe sandbox to scripts-only (removed allow-same-origin)
- Perf-2: Memoized selectAtom in useSetting (prevented new atom ref per render)
- Perf-4: Fixed typingMembers setTimeout leak (tracked timers per user/room)
- Perf-8: Memoized getChatBg() result in RoomView (not inline in JSX)
- Perf-12: Replaced body.class * font-family with body.class (inherited)
- Perf-15: Memoized typingNames array chain in RoomViewTyping
- Perf-9: Added blob URL cleanup useEffect in AudioContent
- BUG: Fixed forEach(async) -> Promise.all in useCommands join handler
- BUG: Fixed useCompositionEndTracking missing dependency array
- A11y: Fixed spoiler button aria-pressed + keyboard handler
- A11y: Added aria-label to Send message button
- Build: Set sourcemap:false, removed netlify.toml from copyFiles

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

src/app/features/room/RoomView.tsx

@@ -1,4 +1,4 @@
-import React, { useCallback, useRef } from 'react';
+import React, { useCallback, useMemo, useRef } from 'react';
 import { Box, Text, config } from 'folds';
 import { EventType } from 'matrix-js-sdk';
 import { ReactEditor } from 'slate-react';
@@ -98,8 +98,13 @@ export function RoomView({ eventId }: { eventId?: string }) {
     )
   );
 
+    const chatBgStyle = useMemo(
+    () => getChatBg(lotusTerminal && chatBackground === 'none' ? 'tactical' : chatBackground, isDark),
+    [chatBackground, lotusTerminal, isDark]
+  );
+
   return (
-    <Page ref={roomViewRef} style={getChatBg(lotusTerminal && chatBackground === 'none' ? 'tactical' : chatBackground, isDark)}>
+    <Page ref={roomViewRef} style={chatBgStyle}>
       <Box grow="Yes" direction="Column">
         <RoomTimeline
           key={roomId}