Use context i18n data automatically with customer account api login

[ruggishop]

WHY are these changes introduced?

The URL generated by the login method of CustomerAccount can receive a uiLocales param used to localize the login page; however it should be possible to pass localization data to the constructor of the CustomerAccount itself, making it less easy to forget.

WHAT is this pull request doing?

1. Pass the language hydrogen context data (from i18n) to createCustomerAccountClient
2. Refactor the ui_locales param building so that it uses the context locale data, overriding it with the data in options.uiLocales is present.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[shopify]

Oxygen deployed a preview of your feat/fr-customer-login-locale branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
third-party-queries-caching	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 12, 202511:09 AM
metaobjects	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 12, 202511:08 AM
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 12, 202511:08 AM
custom-cart-method	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 12, 202511:08 AM
classic-remix	✅ Successful (Logs)	Preview deployment	Inspect deployment	February 12, 202511:09 AM

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