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/RoomTimeline.tsx

@@ -341,7 +341,7 @@ const useTimelinePagination = (
         })
       );
       if (err) {
-        // TODO: handle pagination error.
+        fetching = false;
         return;
       }
       const fetchedTimeline =
@@ -622,7 +622,8 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
             // Check if the document is in focus (user is actively viewing the app),
             // and either there are no unread messages or the latest message is from the current user.
             // If either condition is met, trigger the markAsRead function to send a read receipt.
-            requestAnimationFrame(() => markAsRead(mx, mEvt.getRoomId()!, hideActivity));
+            const _roomId = mEvt.getRoomId();
+          if (_roomId) requestAnimationFrame(() => markAsRead(mx, _roomId, hideActivity));
           }
 
           if (!document.hasFocus() && !unreadInfo) {
@@ -826,7 +827,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
       const evtTimeline = getEventTimeline(room, readUptoEventId);
       const absoluteIndex =
         evtTimeline && getEventIdAbsoluteIndex(linkedTimelines, evtTimeline, readUptoEventId);
-      if (absoluteIndex) {
+      if (typeof absoluteIndex === 'number') {
         scrollToItem(absoluteIndex, {
           behavior: 'instant',
           align: 'start',