fix(a11y): label room page header with room name for screen readers (P3-4)

PageHeader now exposes aria-label="{room name} room header" so screen
reader users know which room's header they are navigating.

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

src/app/features/room/RoomViewHeader.tsx

@@ -524,6 +524,7 @@ export function RoomViewHeader({ callView }: { callView?: boolean }) {
       <PageHeader
         className={ContainerColor({ variant: 'Surface' })}
         balance={screenSize === ScreenSize.Mobile}
+        aria-label={`${name} room header`}
       >
         <Box grow="Yes" gap="300">
           {screenSize === ScreenSize.Mobile && (