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/MembersDrawer.tsx

@@ -89,6 +89,7 @@ function MemberDrawerHeader({ room }: MemberDrawerHeaderProps) {
               <IconButton
                 ref={triggerRef}
                 variant="Background"
+                aria-label="Close member list"
                 onClick={() => setPeopleDrawer(false)}
               >
                 <Icon src={Icons.Cross} />
@@ -360,6 +361,7 @@ export function MembersDrawer({ room, members }: MembersDrawerProps) {
             <ScrollTopContainer scrollRef={scrollRef} anchorRef={scrollTopAnchorRef}>
               <IconButton
                 onClick={() => virtualizer.scrollToOffset(0)}
+                aria-label="Scroll to top"
                 variant="Surface"
                 radii="Pill"
                 outlined