fix(landing): make map switcher and menu toggle keyboard accessible

[olitreadwell]

Motivation

Two of the map viewer's own controls can only be used with a mouse.

They are built from non-interactive HTML elements, so keyboard and screen-reader users cannot reach or operate them:

• The layer switcher (bottom-left mini-map, "Switch map to …") is a plain <div onClick>. It is not in the tab order, does not respond to Enter/Space, and has no button role, so assistive tech does not announce it as a control.
• The header menu toggle (the hamburger / close icon) is a plain <i onClick>. Same problem: not focusable, not keyboard-operable, no role, no accessible name, and no open/closed state exposed.

For a public government map viewer this is a real barrier.

It fails WCAG 2.1 2.1.1 Keyboard (all functionality available from a keyboard) and 4.1.2 Name, Role, Value (controls must expose a name, a role, and their state).

Self-found gap: there is no existing upstream issue for this.

Modifications

• map.switcher.tsx: kept the element a <div> (it wraps another <div>, which is not valid inside a <button>) and made it behave like a button: role="button", tabIndex={0}, an aria-label, and an onKeyDown handler that activates it on Enter and Space (with preventDefault so Space does not scroll the page). The existing click behaviour is unchanged.
• layout.header.tsx: replaced the clickable <i> with a real <button type="button"> wrapping the icon. Added aria-label ("Open menu" / "Close menu") and aria-expanded so the toggle state is announced. The icon is now aria-hidden (decorative). The mouse-only inline cursor: pointer is removed, the button gets it from the existing global rule.
• static/index.css: reset the native chrome on the new menu button so the icon looks exactly as before, and added a :focus-visible outline on the layer switcher so keyboard focus is visible (WCAG 2.4.7 Focus Visible).

One coherent change: make the two custom map controls keyboard-operable and properly labelled.

No behaviour change for existing mouse users.

How to verify

Ran in packages/landing on Node 24:

git fetch https://github.com/olitreadwell/basemaps.git fix/landing-a11y-keyboard-controls
git checkout FETCH_HEAD
npm install
npm run build      # tsc -b: clean
npm run test       # 27 passed, 0 failed
npx eslint packages/landing/src/components/map.switcher.tsx \
           packages/landing/src/components/layout.header.tsx   # clean

Accessibility, reasoned per control (before → after):

• Layer switcher: before: not in tab order, no role, Enter/Space do nothing, name only via title (not a reliable accessible name). After: reachable by Tab, announced as "Switch map to …, button", operable with Enter and Space, visible focus ring.
• Menu toggle: before: <i> not focusable, no role/name/state. After, a real <button>, in the tab order, announced as "Open menu, button" / "Close menu, button" with expanded/collapsed state, Enter/Space work natively.

The repo has no component-DOM test harness (tests run via node --test on compiled JS, no jsdom/testing-library), so this is verified by build + lint + type-check + the existing suite staying green, plus the concrete control-by-control reasoning abov: not by a new UI test.

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AI disclosure: Drafted with AI assistance.

I found the gap, verified the fix against the current code, ran the build/lint/tests, and reviewed the diff line by line.

AI code review (open-code-review, delegation mode): clean.

Promote upstream with:

gh pr create --repo linz/basemaps --base master --head olitreadwell:fix/landing-a11y-keyboard-controls-20260805-040920

No CLA, DCO, or commit signing is required by this repo.

Commit message and this PR title follow Conventional Commits, matching the repo's PR-title lint.

AI assistance

Drafted with AI assistance. The change was verified before opening, and the diff was reviewed line by line.

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PROMOTION NOTE (remove this section before/when opening against upstream):

Open the compare view to create the upstream PR (scoped to this branch):

linz/basemaps@master...olitreadwell:basemaps:fix/landing-a11y-keyboard-controls

Or via CLI:

gh pr create --repo linz/basemaps --base master --head olitreadwell:fix/landing-a11y-keyboard-controls

Prerequisites: none outstanding (re-verify CLA/DCO/signing before promoting).