Type check the js files that have JSDocs

We have files like `bin/l10n-sync.js` that have JSDocs in them, but apparently we are not checking them with `yarn ts` correctly. See my comment here: https://github.com/firefox-devtools/profiler/pull/5659#issuecomment-3498430787

It would be good to properly check them with typescript. To be able to do that I believe we need to add `"allowJs": true` to tsconfig.json, and add `// @ts-check` to these files.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-940)