Menu locale fixes

[zorkow]

Fix German menu localisation and restructure locale IDs

PR refines the menu localisation system introduced in feature/locale-components, fixes the German menu
translations, and adds a new dedicated locale component for ARIA role descriptions.

Changes

German menu localisation fix

• Corrected German translations across ts/ui/menu/__locales__/de.json that did not sound quite right to my ear. Also ensures they are not too long.

Locale ID restructuring

• Most menu locale keys are now namespaced with a category prefix. This makes the key hierarchy explicit and gives context during localisation. As discussed I reversed Title for Help and Clearspeak.

New a11y locale component (ts/a11y/__locales__/)

• Component.ts registers the a11y locale component and exposes a localize() helper.
• en.json / de.json provide English and German strings for ARIA role descriptions.
• Matching components/mjs/a11y/ bundle files wire the component into the build.

**New aria.ts module and new a11y locale component **

• ts/a11y/aria.ts introduces AriaRoleDescription with keys for all role description variants we want to localize.
• localizeAria(id) resolves an ARIA key through the locale system, falls to the id as "localised" string. This is important when a description is explicitly defined in the menu options.
• Menu.ts now uses AriaRoleDescription.* constants instead of bare string literals for the role-description radio
  group and its default value.
• The radio() helper in Menu.ts routes ARIA keys through localizeAria() so they are localised correctly.

** Other things **

• Locale.ts needed a fixed for missing initialised field.
• There are a couple of your commits in the PR: for bussproofs locale and Clipboard-copy error in MenuUtil.ts.

I am not sure if it is worthwhile to rebase and reply my commits or if this comes out in the wash once all the other branches have landed on feature/locale