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/state/typingMembers.ts

@@ -89,27 +89,34 @@ export const roomIdToTypingMembersAtom = atom<
 
       // remove typing receipt after some timeout
       // to prevent stuck typing members
-      setTimeout(() => {
-        const { roomId, userId } = action;
-        const timeout = timeoutReceipt(
-          get(baseRoomIdToTypingMembersAtom),
-          roomId,
-          userId,
-          TYPING_TIMEOUT_MS
-        );
-        if (timeout) {
-          set(
-            baseRoomIdToTypingMembersAtom,
-            produce(get(baseRoomIdToTypingMembersAtom), (draft) =>
-              deleteTypingMember(draft, {
-                type: 'DELETE',
-                roomId,
-                userId,
-              })
-            )
+      const timerKey = `${action.roomId}:${action.userId}`;
+      const existingTimer = typingTimers.get(timerKey);
+      if (existingTimer !== undefined) clearTimeout(existingTimer);
+      typingTimers.set(
+        timerKey,
+        setTimeout(() => {
+          typingTimers.delete(timerKey);
+          const { roomId, userId } = action;
+          const timeout = timeoutReceipt(
+            get(baseRoomIdToTypingMembersAtom),
+            roomId,
+            userId,
+            TYPING_TIMEOUT_MS
           );
-        }
-      }, TYPING_TIMEOUT_MS);
+          if (timeout) {
+            set(
+              baseRoomIdToTypingMembersAtom,
+              produce(get(baseRoomIdToTypingMembersAtom), (draft) =>
+                deleteTypingMember(draft, {
+                  type: 'DELETE',
+                  roomId,
+                  userId,
+                })
+              )
+            );
+          }
+        }, TYPING_TIMEOUT_MS)
+      );
     }
 
     if (