fix: Use useTranslation() hook server-side for proper i18n SSR

[baptistegrimaud]

Fixes #317.

Description

Use useTranslation() hook in server components: Replaced direct import { t } from "i18next" with usage of useTranslation() hook in all React server components (HelloWorld, LanguageSwitcher, etc.). This ensures translations are context-aware and avoid hydration mismatches between server and client.

Also, explicitly set the default namespace (defaultNS) in I18nextProvider wrapper to ensure proper translation loading for multiple modules on the same page. Its value is the bundle key (symbolic name).

Testing

Enhance the existing Cypress test with components from multiple JS modules on the same page, to validate:

• 2 components from hydrogen module render server-side translations
• 2 components from javascript-modules-engine-test-module render server-side translations
• All client-side translations hydrate and update correctly

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Pull request overview

This PR addresses i18n conflicts when rendering multiple JavaScript modules on the same page by ensuring translations resolve against the correct module namespace during SSR and hydration (Issue #317).

Changes:

• Replace direct t usage from the i18next singleton with useTranslation() in server-rendered React components (samples and template).
• Set defaultNS on I18nextProvider during SSR (view renderer + islands) so useTranslation() defaults to the module bundle key namespace.
• Extend the Cypress i18n E2E test to validate SSR + hydration behavior with components from two different modules on the same page.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/cypress/e2e/ui/testI18n.cy.ts	Expands E2E coverage to assert SSR + hydrated translations for multiple modules on one page.
samples/hydrogen/src/components/LanguageSwitcher/default.server.tsx	Switches server component translation usage to useTranslation() for context-aware SSR.
samples/hydrogen/src/components/HelloWorld/default.server.tsx	Switches server component translation usage to useTranslation() for context-aware SSR.
javascript-modules-library/src/components/render/Island.tsx	Provides defaultNS={bundleKey} to scope translations correctly within islands during SSR.
javascript-modules-engine/src/server/init-react.tsx	Provides defaultNS={bundleKey} during SSR view rendering (and stops mutating global default namespace).
javascript-create-module/templates/hello-world/src/components/Hello/World/default.server.tsx	Updates template server component to use useTranslation() to match the new SSR i18n approach.

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