chore: Add locale validation script to GitHub CI

[O2sa]

The repository already includes a locales validation script (scripts/validate-locales.js), but it is not yet part of the GitHub CI workflow. Adding it to CI will ensure new locale files stay consistent with the English source and prevent broken or incomplete locale merges.

Tasks

• Inspect scripts/validate-locales.js and confirm it runs correctly in a CI environment.
• Add a GitHub Actions workflow step that runs the locales validation script before tests or after linting.
• Ensure failures are reported clearly in GitHub CI when locale files are missing keys or contain invalid JSON.

Notes

• The validation should run on pull requests and main branch CI, not just local developer scripts.
• If necessary, add a lightweight npm or pnpm script entry for easier execution (pnpm validate-locales), then use that script in the workflow.

Tip

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