Make react and lingui eager module-federation singletons to stabilize the federated i18n context

[raix]

Summary & Motivation

Make the federated translation context a single instance so a federated component's useLingui can no longer throw used without I18nProvider on a direct or reloaded page load.

• Root cause, detected empirically: despite singleton: true, @lingui/core and @lingui/react were duplicated at runtime — a probe recorded two distinct i18n/LinguiContext/useLingui instances across the remote loads. A remote consumed early on a direct load (account's AuthSyncModal via the withSystemTranslations gate) fell back to its own bundled copy, getting a second LinguiContext with no provider. react/react-dom were not duplicated (pluginReact handles those), which is why only the Lingui path broke.
• The change marks react, react-dom, @lingui/core, and @lingui/react as eager singletons in the module-federation shared map (in ModuleFederationPlugin.ts). eager places them in the shared scope during the host's synchronous startup, before any remote consumes them, so there is no per-remote fallback copy. The four are required together — eager Lingui synchronously requires react, so react/react-dom must be eager too. @tanstack/react-router and @tanstack/react-query stay non-eager singletons.

Checklist

• I have added tests, or done manual regression tests
• I have updated the documentation, if necessary