[WS-1858] SPIKE: Sign in - Implement IDCTA in WS Front End

[elvinasv]

Resolves JIRA: https://bbc.atlassian.net/browse/WS-1858

Summary

We’re adding a first “BBC Account” (IDCTA) integration to the World Service FE as an MVP, so WS pages can show the right account actions (e.g. Sign in / Register and an Account entry point when signed in).

To do this, the app now:

• Fetches the IDCTA configuration server-side (SSR)
• Stores that config in a new Account Provider, making it available to any WS components that need it
• Renders Account-related UI components (e.g. account buttons/links) using that provider data, as a minimal, working MVP that fits into the existing WS masthead/layout (with minimal refactoring)

Developer Checklist

• UX
  • UX Criteria met (visual UX & screenreader UX)
• Accessibility
  • Accessibility Acceptance Criteria met
  • Accessibility swarm completed
  • Component Health updated
  • P1 accessibility bugs resolved
  • P2/P3 accessibility bugs planned (if not resolved)
• Security
  • Security issues addressed
  • Threat Model updated
• Documentation
  • Docs updated (runbook, READMEs)
• Testing
  • Feature tested on relevant environments
• Comms
  • Relevant parties notified of changes

Testing

• Manual Testing required?
  • Local (Ready-For-Test, Local)
  • Test (Ready-For-Test, Test)
  • Preview (Ready-For-Test, Preview)
  • Live (Ready-For-Test, Live)
• Manual Testing complete?
  • Local
  • Test
  • Preview
  • Live

Additional Testing Steps

1. List the steps required to test this PR.

Useful Links

• Coding Standards
• Repository use guidelines
• Add Links to useful resources related to this PR if applicable.