A tab's profile was only discoverable by opening the three-dot menu, which is
a poor place for something that changes what you are logged into.

The chrome row gains a leading slot before the URL bar, and the preview names
the tab's profile there. Only when it differs from the default: labelling
every tab "Default" would be noise on the common case, while a tab running in
another profile is exactly what needs calling out.

Also gives the three-dot menu's profile heading a `MenuGroup` ancestor —
`MenuGroupLabel` reads Base UI's group context and throws without one, which
took the app to its error boundary as soon as the menu opened.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>