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/components/message/FileHeader.tsx

@@ -48,6 +48,7 @@ export function FileDownloadButton({ filename, url, mimeType, encInfo }: FileDow
       variant={hasError ? 'Critical' : 'SurfaceVariant'}
       size="300"
       radii="300"
+      aria-label={downloading ? 'Downloading...' : hasError ? 'Download failed, click to retry' : 'Download file'}
     >
       {downloading ? (
         <Spinner size="100" variant={hasError ? 'Critical' : 'Secondary'} />

src/app/components/message/content/AudioContent.tsx

@@ -173,6 +173,7 @@ export function AudioContent({
           size="300"
           radii="Pill"
           onClick={() => setMute(!mute)}
+          aria-label={mute ? 'Unmute' : 'Mute'}
           aria-pressed={mute}
         >
           <Icon src={mute ? Icons.VolumeMute : Icons.VolumeHigh} size="50" />