fix(sidebar): scroll to the active item after navigating

[brandyscarney]

Problem:
When navigating the docs site, the sidebar does not update to reflect the active item.

Solution:
This PR updates the sidebar to scroll the active item into view when a new page is selected.

Test steps:

1. Visit https://ionicframework.com/docs/components
2. Scroll down and select "Popover"
3. Notice that the sidebar remains at the top (starting at "Accordion") and "Popover" is not visible
4. Visit https://ionic-docs-git-fix-sidebar-scroll-ionic1.vercel.app/docs/components
5. Repeat step 2
6. Confirm that the sidebar now scrolls to and highlights "Popover"

Repeat the test steps above for a "Guide" page:

1. Go to https://ionicframework.com/docs/
2. Click on the "Theming" card
3. Notice the sidebar remains at the top
4. Repeat for https://ionic-docs-git-fix-sidebar-scroll-ionic1.vercel.app/docs/

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
ionic-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 22, 2025 6:51pm

[ShaneK]

Nice!