feat: frontend-base i18n support

[brian-smith-tcril]

• Part of i18n pipeline frontend-base#176

Three changes to wire up frontend-base i18n support in this app, per the migration guide:

1. Add atlasTranslations to package.json

Adds an atlasTranslations field so that sites using openedx translations:pull can resolve and pull this app's translations transitively, and so the app can pull its own translations when running in dev mode.

"atlasTranslations": {
  "path": "translations/frontend-app-authn/src/i18n/messages",
  "dependencies": ["@openedx/frontend-base"]
}

2. Switch pull_translations to use openedx translations:pull

Replaces the old Makefile atlas pull commands with npm run translations:pull (backed by openedx translations:pull), passing ATLAS_OPTIONS through. Also removes the placeholder messages object from src/i18n/index.js and the manual messages import in src/app.ts — translations are now handled by the frontend-base i18n pipeline.

Also removes the unused intl_imports and i18n Makefile variables and the detect_changed_source_translations target (confirmed unused by any CI workflow or translation-related target).

3. Add src/i18n/index.ts and src/i18n/messages.d.ts

Renames src/i18n/index.js → index.ts (the project uses TypeScript) and adds a messages.d.ts type declaration stub so TypeScript is satisfied before translations:pull has been run.

Before merging

• feat: add translations: CLI commands and update runtime i18n integration frontend-base#205 must land first (landed as 1.0.0-alpha.23)
• Verify that npm run dev (the app's own dev site) can pull and load translations correctly
  • With workspaced frontend-base from the feat: add translations: CLI commands and update runtime i18n integration frontend-base#205 branch
  • With installed frontend-base after feat: add translations: CLI commands and update runtime i18n integration frontend-base#205 lands

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.12%. Comparing base (ffe7e18) to head (9414b9f).
⚠️ Report is 5 commits behind head on frontend-base.

Additional details and impacted files

@@              Coverage Diff               @@
##           frontend-base    #1661   +/-   ##
==============================================
  Coverage          92.12%   92.12%           
==============================================
  Files                 92       92           
  Lines               2045     2045           
  Branches             577      588   +11     
==============================================
  Hits                1884     1884           
  Misses               158      158           
  Partials               3        3           

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[openedx-semantic-release-bot]

🎉 This PR is included in version 1.0.0-alpha.8 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀