Domain visibility for multi-site setups

The page.url.domain attribute is now surfaced in three places for multi-site web integrations:

• Session list sidebar: Domain shown alongside location and browser info.
• Session detail page: Domain appears in the header for quick context.
• Dashboard filters: New Domain filter variable available in Overview and Web Vitals dashboards.

Also: session detail header items now wrap gracefully on smaller screens instead of getting squeezed.