Stop route changes from animating scroll position

[DanPiazza-Netwrix]

Summary

• Global scroll-behavior: smooth (src/css/custom.css) made every page navigation visibly animate scroll-to-top/anchor instead of snapping, since Docusaurus resets scroll position via window.scrollTo/scrollIntoView on each route change
• Added src/clientModules/scrollBehavior.js, registered via clientModules in docusaurus.config.js, that disables smooth scrolling for cross-page navigation while preserving it for same-page anchor clicks (TOC links, etc.)
• Also handles a fresh full-page load to a hash URL (target element doesn't exist yet in the dev server's client-rendered shell) and waits for layout to settle before scrolling so anchors land clear of the sticky navbar

Test plan

• Navigate to a new page with no anchor — lands at top instantly
• Navigate (fresh load and in-app) to a new page with an anchor — lands at the anchor instantly, clear of the sticky navbar
• Click a TOC/anchor link while already on the page — still animates smoothly

[github-actions]

Code Review

Reviewed for correctness (bugs, security, build/routing, workflows) — documentation/style excluded per scope.

No issues found. This is a clean, well-contained change.

Notes from the review:

• docusaurus.config.js — clientModules is a valid top-level config field, and the referenced path ./src/clientModules/scrollBehavior.js exists. No build/routing risk.
• SSR safety — the module has no top-level side effects (only function declarations), so its SSR import is harmless; onRouteUpdate/onRouteDidUpdate are client-only lifecycle hooks, so document/window are never touched during the build.
• No temporal-dead-zone bug — cleanup() references stopTimer and observer (declared later with const), but it is only ever invoked asynchronously from timer/observer callbacks, after synchronous initialization completes, so the bindings are initialized by then.
• No leaks — the MutationObserver and both timers are unconditionally torn down by the 2s stopTimer, and attemptScroll cleans up early once the hash matches. The attributes: true, subtree: true observation is broad but bounded to the fresh-hash-load path and capped at 2s.
• Behavior logic — behavior: 'instant' is a valid ScrollBehavior value, and the smooth/auto inline-style toggling is consistent with the global scroll-behavior: smooth in src/css/custom.css. Same-page anchor nav keeps smooth; cross-page nav snaps.