feat: persist sidebar scroll position across page navigations #74

Problem

The sidebar navigation currently resets to the top every time the user navigates between pages.
For readers working through content in sections deep in the sidebar (e.g. Node-API, Diagnostics,
or Asynchronous Work), this means manually scrolling back down after every page visit — which creates
a frustrating and disorienting experience.

Additionally, SideBar from @node-core/ui-components does not support forwardRef, so passing
ref={sidebarRef} to it is silently ignored. This means the scroll restoration logic in
useScrollToElement and useScroll never receives a valid DOM reference to attach the scroll listener to.

Proposed Solution

1. Fix ref acquisition – Use useLayoutEffect in Sidebar/index.jsx to manually assign sidebarRef.current
   to the rendered <aside> element before useEffects run, ensuring the scroll listener is properly attached.

2. Persist scroll position – Extend useScrollToElement to:

   • Save the sidebar scroll position to localStorage on every scroll event (debounced).
   • On mount, restore from NavigationStateContext (same-session navigation) or fall back to localStorage
     (full page refresh), whichever is available.

Files Changed

• components/Sidebar/index.jsx – use useLayoutEffect to acquire ref to <aside>
• hooks/useScrollToElement.js – add localStorage read on mount and write on scroll
• hooks/useScroll.js – use onScrollRef pattern to avoid stale closure on onScroll callback

Expected Behaviour

Action	Before	After
Navigate to another page	Sidebar resets to top	Sidebar stays at last scroll position
Hard refresh (F5)	Sidebar resets to top	Sidebar restores from localStorage

Notes

• SideBar from @node-core/ui-components needs to support forwardRef for this to work without
  the useLayoutEffect workaround. A separate issue/PR upstream on that package may be worth considering.
• The useScroll hook dependency on ref.current (instead of ref) ensures the listener is attached
  after the DOM element is available.