fix(video): keep scroll position and stop pause from going fullscreen

- VideoBubble: stopPropagation on the inline <video> element so
  clicks on the native controls (play/pause/seek) don't bubble up
  to the outer tile, which previously promoted any control click
  into a fullscreen overlay.
- VideoPlayer: replace overflow:hidden body lock with the iOS-safe
  position-fixed + scroll-restore pattern. Closing the fullscreen
  player now returns the page to the exact scroll offset it had,
  instead of snapping back to the top on iOS Safari.

src/components/messageStream/bubbles/VideoBubble.tsx

@@ -87,6 +87,7 @@ function VideoAttachmentCard({
             controls
             playsInline
             autoPlay
+            onClick={(e) => e.stopPropagation()}
             className="absolute inset-0 h-full w-full"
           />
           <AttachmentDownloadPill