platform.bible-extension: use EthnoLib for language-tag entry in Create Lexicon form

Problem

In the Create Lexicon form (platform.bible-extension/src/components/create-lexicon.tsx), the vernacular and analysis writing-system fields are plain text inputs — users must type a raw IETF/BCP-47 language tag (e.g. es-MX) from memory. Validity is only checked after the fact, via a regex fallback plus Intl.getCanonicalLocales (see isValidLangTag/BASIC_IETF_LANGUAGE_TAG_PATTERN, create-lexicon.tsx:11-27). This is error-prone for anyone who doesn't already know BCP-47 syntax by heart.

EthnoLib provides exactly this kind of language picker as a reusable, langtags.json-backed utility: fuzzy search by language name/autonym, with script/region disambiguation, producing a well-formed tag.

Proposal

• Skip @ethnolib/language-chooser-react-mui (the only ready-made drop-in UI) — it hard-requires MUI 5 + Emotion and peer-depends on React ^17.0.2, while this repo/paranext-core is on React ^19.0.0. Pulling it in would also add a second UI system alongside the Tailwind/shadcn components (platform-bible-react) already used throughout the extension.
• Instead use the headless pieces:
  • @ethnolib/find-language — fuzzy search + tag utilities (e.g. getShortestSufficientLangtag), no UI framework dependency.
  • @ethnolib/language-chooser-react-hook — React hook wrapping the above into search/select state; declares no hard React peer version, so it works under React 19.
• Render results with platform-bible-react's existing Popover + Command primitives (already used elsewhere in this codebase) as a searchable combobox, rather than adopting MUI.
• Add a new shared component, e.g. src/components/language-tag-picker.tsx, and use it for the vernacularWs/analysisWs fields in create-lexicon.tsx (the name/code fields are unaffected).
• Keep a manual-entry fallback for tags outside the database (the hook supports this via customizableLanguageDetails), so the existing isValidLangTag/normalizeLangTag validation stays in place for that path rather than being deleted.

Scope

• New deps: @ethnolib/find-language, @ethnolib/language-chooser-react-hook (MIT, no MUI/Emotion).
• Touches only platform.bible-extension/src/components/create-lexicon.tsx plus the new picker component.

Start with platform.bible-extension/src/components/create-lexicon.tsx, especially the vernacularWs and analysisWs fields and existing language-tag validation, then inspect how platform.bible-react's Popover and Command primitives are used elsewhere. Add the shared language-tag picker with EthnoLib search and selection, retain manual entry for unsupported tags, and confirm both Create Lexicon fields produce valid tags.