Docs: add active sidebar section tracking

[RinshaAk]

Summary

Adds active section tracking to the documentation sidebar.

What changed

• Track the visible h2/h3 heading with IntersectionObserver.
• Highlight the corresponding sidebar anchor.
• Update the active section immediately when a sidebar anchor is clicked.
• Automatically scroll the active sidebar anchor into view.
• Reset the active section when navigating to another documentation page.
• Add aria-current and smooth color transitions for the active anchor.
• Scope active anchor highlighting to the current page.

Tests

• ESLint passes for the touched components.
• Focused Page and SidebarItem tests pass.
• Updated SidebarItem snapshot.

Notes

The full Jest suite has existing ESM/Jest configuration failures unrelated to this change.

Use of AI

AI assistance was used during development to help debug the implementation, review code changes, and improve tests. All changes were reviewed and tested locally before submission.

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Project	Deployment	Actions	Updated (UTC)
webpack-js-org	Ready	Preview	Aug 13, 2026 3:13pm