ui 0.6.0: shared AppearanceControl, LanguageOptions and PreferencesMenu

[rrolf]

For virtUOS/ausleihbar#35. AbstimmBAR can switch over later, and the nearly line-for-line identical code in both tools goes away.

New in @basicbar/ui 0.6.0

• AppearanceControl(): Auto / Light / Dark as a labelled role="group" of menuitemradio rows with aria-checked. State comes from useTheme().
• LanguageOptions({ onChange?, onPicked?, heading? }): one menuitemradio row per supported language, in its own labelled group.
  • No "Auto" entry. Until the user picks a language, the UI follows the system (i18next detector), and the list marks the language actually shown.
  • A pick is binding: i18next caches it. The app can also store it server-side via onChange, for example for emails.
• PreferencesMenu({ onLanguageChange? }): a round preferences button (SlidersHorizontal, aria-label "Preferences", aria-haspopup/aria-expanded) opening a menu with language and appearance, split by a role="separator".
  • It closes on an outside click, on Escape and after a language pick, and focus returns to the button.
  • It is meant for logged-out visitors. In account menus, LanguageOptions and AppearanceControl are placed directly.
• README: a new section, and the Tailwind content example now includes ./node_modules/@basicbar/ui/dist/**/*.js. Without it the component classes are missing in the consumer.
• CHANGELOG: ui 0.6.0, additive. Consumers add the translation key "Preferences".

Tests

• npm run build and tsc --noEmit pass.
• Ausleihbar was checked with the packed tgz:
  • Signed-in account menu: "Sprache" and "Darstellung" groups; switching the language changes the UI and saves it in the browser (lang) and on the account.
  • Logged-out header: "Anmelden" and "Einstellungen"; Escape closes, focus returns.
  • At 390 px the header fits without horizontal scrolling.

Release after merge

Tag ui/v0.6.0.

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