fix(a11y,bug): aria-labels on dialogs/buttons, useAlive GIF guard, typing timer fix

A11y:
- Add aria-label Close to RoomTopicViewer, ImagePackView close buttons
- Add aria-label Cancel to LeaveRoomPrompt cancel button
- Add aria-label to Send, Reply, Thread, Edit, React, Search, Mute, Download buttons
- Fix aria-pressed -> aria-expanded + aria-haspopup on menu anchor triggers
- Add aria-label to username/password auth inputs

BUG-21: Add useAlive unmount guard to handleGifSelect error path in RoomInput
BUG-22: Fix typing status timer accumulation with typingTimerRef

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

src/app/features/room/RoomViewHeader.tsx

@@ -532,7 +532,7 @@ export function RoomViewHeader({ callView }: { callView?: boolean }) {
               }
             >
               {(triggerRef) => (
-                <IconButton fill="None" ref={triggerRef} onClick={handleSearchClick}>
+                <IconButton fill="None" ref={triggerRef} onClick={handleSearchClick} aria-label="Search">
                   <Icon size="400" src={Icons.Search} />
                 </IconButton>
               )}