fix: scroll active sidebar items into view

[angelplusultra]

Pull Request Type

• ✨ feat
• 🐛 fix
• ♻️ refactor
• 💄 style
• 🔨 chore
• 📝 docs

Relevant Issues

resolves #4963

What is in this change?

This PR fixes the sidebar selection scroll behavior so that active items are automatically scrolled into view when selected.

Changes:

• Added a new reusable hook useScrollActiveItemIntoView that handles scrolling an element into the viewport when it becomes active
• Applied the hook to MenuOption in the Settings Sidebar so the currently selected setting is scrolled to center view
• Applied the hook to ThreadItem in the main Sidebar so the active thread is scrolled to center view
• Uses behavior: "instant" to avoid visible scroll animation artifacts (since sidebars remount on navigation, smooth scrolling would animate from the top)

Additional Information

The instant behavior is used intentionally because the Settings Sidebar remounts on each page navigation. Using smooth would cause a visible scroll animation from the top of the sidebar to the active item every time you navigate.

Developer Validations

• I ran yarn lint from the root of the repo & committed changes
• Relevant documentation has been updated
• I have tested my code functionality
• Docker build succeeds locally

[shatfield4]

LGTM, we can reuse this hook in the future on the main chat sidebar to scroll into view the active workspace if a user has a lot of workspaces.