feat(a11y): comprehensive icon button label sweep — 60+ remaining buttons labeled

C-1 complete sweep across all components and features:
- Call controls: mic mute/unmute, deafen/undeafen, video, screenshare, chat
- RoomInput: dismiss reply, attach file, sticker, emoji, GIF, location, toolbar
- Media viewers: close in image/pdf/text viewers and editors
- Settings dialogs: close buttons in all room/space/common settings panels
- Lobby: back, toggle member list, scroll to top, pack add/remove
- Auth: server picker, UIA flow cancel
- Upload cards: cancel uploads
- URL preview: prev/next buttons
- Members drawer: close + scroll to top
- RoomViewHeader: back, start call, toggle member list

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

src/app/features/room/room-pin-menu/RoomPinMenu.tsx

@@ -146,6 +146,7 @@ function PinnedMessage({
       </Chip>
       {canPinEvent && (
         <IconButton
+          aria-label="Pinned messages"
           data-event-id={eventId}
           variant="Secondary"
           size="300"
@@ -457,7 +458,7 @@ export const RoomPinMenu = forwardRef<HTMLDivElement, RoomPinMenuProps>(
               <Text size="H5">Pinned Messages</Text>
             </Box>
             <Box shrink="No">
-              <IconButton size="300" onClick={requestClose} radii="300">
+              <IconButton size="300" onClick={requestClose} radii="300" aria-label="Close">
                 <Icon src={Icons.Cross} size="400" />
               </IconButton>
             </Box>