feat: frontend-base i18n support

[brian-smith-tcril]

• Part of i18n pipeline frontend-base#176

Four 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-learner-dashboard/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 unused intl_imports, i18n, ATLAS_EXTRA_SOURCES, and ATLAS_EXTRA_INTL_IMPORTS 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 replaces the placeholder messages object with a clean re-export from ./messages. Adds a messages.d.ts type declaration stub so TypeScript is satisfied before translations:pull has been run.

4. Remove App.messages from src/app.ts

Removes the messages import and field from the app config — App.messages was removed from the App type in frontend-base. Translations are now handled by the frontend-base i18n pipeline via site.i18n.

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

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (frontend-base@08b54cd). Learn more about missing BASE report.

Additional details and impacted files

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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

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