fix(legacy-html): prevent scroll jump when opening header pickers

[Sahilshrma31]

Description

Fixes an unintended page scroll jump when opening sticky header picker dropdowns in legacy HTML docs.

Validation

I reproduced and verified on a generated legacy HTML page (out/fs.html) and in browser behavior matching the reported scenario.

Reproduction steps

Open an API docs page.
Scroll to the middle of the page.
Open sticky header pickers (Table of contents, Index, Other versions, Options).

Before

Screen.Recording.2026-04-15.at.11.01.24.PM.mov

Opening a picker causes the page to jump upward unexpectedly.

After

Screen.Recording.2026-04-15.at.11.02.03.PM.mov

Opening a picker no longer changes scroll position; only the dropdown opens.

Related Issues

Fixes #764

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run node --run test and all tests passed.
• I have check code formatting with node --run format & node --run lint.
• I've covered new added functionality with unit tests if necessary.

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Project	Deployment	Actions	Updated (UTC)
api-docs-tooling	Ready	Preview	Apr 15, 2026 5:37pm

[cursor]

PR Summary

Low Risk
Low risk: small client-side UI tweak limited to legacy HTML picker focus behavior, with a guarded fallback for browsers that don’t support preventScroll.

Overview
Prevents an unintended scroll jump when opening legacy HTML header picker dropdowns by focusing the first dropdown link with focus({ preventScroll: true }).

Adds a null check and a try/catch fallback to plain focus() for browsers that don’t support the preventScroll option.

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