Make the pages dropdown an accessible disclosure control

[reakaleek]

Problem

The Lighthouse target-size audit fails on the current-section link in the sidebar pages dropdown:

div#pages-dropdown > button.w-full > div > a.pages-dropdown_active
Target: 96.9 px × 21.5 px; required safe target: at least 24 px × 24 px

The markup also places an <a> inside a <button>, which is invalid nested interactive content. The dropdown is opened through CSS :focus-within, has no aria-expanded/aria-controls state, and requires a mousedown focus workaround.

Relevant code

• src/Elastic.Documentation.Site/Navigation/_TocTree.cshtml
• src/Elastic.Documentation.Site/Assets/pages-nav.ts
• src/Elastic.Documentation.Site/synthetics/journeys/navigation-test.journey.ts

Proposed implementation

1. Replace the nested button > a structure with sibling controls in one row:
   • a full-height current-section link with a minimum 24 px target;
   • a dedicated disclosure button for the chevron.
2. Give the button type="button", aria-expanded, and aria-controls pointing to a stable menu ID.
3. Remove tabindex="0" from the non-interactive wrapper.
4. Manage open/close explicitly in pages-nav.ts, including Space/Enter through native button behavior, Escape to close and restore focus, outside click/focus, and state synchronization after htmx navigation.
5. Remove preventFocusLossOnLinkClick; it should no longer be needed.

Acceptance criteria

• No interactive element contains another interactive element.
• Both the current-section link and disclosure button have a target of at least 24 px × 24 px.
• aria-expanded accurately reflects menu visibility and aria-controls references the menu.
• Keyboard users can open, close, navigate, and Escape from the menu.
• Existing link preloading and htmx navigation continue to work.
• Jest tests cover open/close, Escape, and ARIA state.
• The synthetic navigation journey uses the disclosure button by role and still reaches /docs/reference.
• Lighthouse no longer reports the pages-dropdown target-size failure.