Fix scrollToComposer scrolling the window

[zattak1]

Summary

• scrollToComposer calls scrollIntoView/scrollIntoViewIfNeeded on the chat composer element, which can scroll any ancestor — including the window — when the chat tool is inside a newly pushed column that hasn't established its own scroll context yet
• This causes the page to jump to the footer when opening a Conversation panel from an event details page, creating a janky experience and hiding the close button
• Fix: save and restore window.scrollY around the scrollIntoView calls so only the chat's internal container scrolls

Test plan

• Open an event details page in a Communities app
• Click the Conversation button to open the chat column
• Verify the page does NOT scroll to the footer
• Verify the chat composer is still visible and scrolled into view within its own column
• Verify sending messages and receiving messages still auto-scroll within the chat column

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