feat(app): add Korean (ko) locale support

[moduvoice]

Motivation

This adds Korean (ko) translation support — to help Korean-speaking users use this
open-source project more comfortably in their own language.

한국 사람들의 오픈소스 이용에 도움이 되게 하기 위해서 한글화 작업을 하였습니다.

Changes

• packages/app/gatsby-config.js: registered ko in the gatsby-plugin-react-i18next languages array (['en', 'ja', 'ko'])
• packages/app/src/locales/ko/common.json (new): full Korean translation, 83/83 keys, 1:1 parity with en/ja (all {{version}} interpolation tokens, $t(...) cross-references, and <br>/<br /> tags preserved in position and count)
• packages/app/src/locales/en/common.json and packages/app/src/locales/ja/common.json: added "ko": "한국어" to the language display-name map
• .changeset/warm-lions-add.md: changeset for @viron/app (minor), following the repo's existing changeset convention

No changes were needed in the language switcher component (packages/app/src/components/app-sidebar.tsx) — it renders language options dynamically from the languages array provided by the i18n hook, so registering ko in gatsby-config.js plus the language.ko key is sufficient for it to appear automatically.

Scope note: example/nodejs/src/locales (a small demo backend locale, unrelated to the admin-dashboard UI i18n registry) and packages/website/i18n (the separate Docusaurus documentation site, ~35 files) were intentionally left untouched, since this PR focuses on the admin-dashboard UI. Happy to follow up with either as a separate PR if maintainers want it.

Testing

• Programmatic key-parity check: 83/83 keys present in ko/common.json, 0 missing/extra vs both en and ja; all {{version}} tokens, $t(...) references, and <br>/<br /> tags verified byte-identical in position/count.
• Ran npx gatsby build (Node 22, per packages/app's engines field) end-to-end: build succeeded, and the output under public/ko/* contains a full set of statically generated Korean routes (index, 404, endpoints, endpointimport, oauthredirect, oidcredirect, dashboard/endpoints, dashboard/groups, endpoints/[endpointId] — matching the existing /ja/* route count 1:1). public/index.html's language switcher <select> renders <option value="ko">한국어</option> alongside en/ja, confirming the new locale is genuinely reachable in the built UI.
• eslint (workspace's own npm run lint in packages/app): 0 errors, 112 warnings (pre-existing, unrelated to this change).
• prettier --check on all changed files: passes.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4241448

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@viron/app	Minor

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