fix(agents): Repaint the conversation after editing a message

Cancelling an edit of an earlier message left a blank gap where the message
was, and while editing, the entries below could keep half of their old
pixels. The webview didn't repaint conversation entries under
content-visibility: auto after their layout changed. Entries now always
render.

src/features/agents/Session.module.css

@@ -117,11 +117,6 @@
 .stream:focus {
   outline: none;
 }
-/* Off-screen entries skip layout, so resizing the pane doesn't reflow a long conversation. */
-.stream > * {
-  content-visibility: auto;
-  contain-intrinsic-block-size: auto 80px;
-}
 
 /* Your message with its actions, shown on hover. */
 .message {