fix: Update frontend workflows to catch TypeScript errors

[neubig]

This PR fixes issue #5343 where frontend TypeScript errors cause Python unit tests to fail but not frontend workflows.

Changes:

1. First commit: Introduced a TypeScript error to reproduce the issue

   • Removed null check from textareaRef.current to trigger TypeScript error
   • Verified that Python tests fail but frontend tests pass

2. Second commit: Added TypeScript compilation to frontend workflows

   • Added npm run make-i18n && tsc to frontend unit tests workflow
   • Added TypeScript compilation to lint workflow
   • This ensures TypeScript errors are caught by frontend-specific workflows

3. Third commit: Fixed the TypeScript error

   • Added proper null check for textareaRef.current
   • Verified all workflows pass

These changes ensure that:

1. TypeScript errors are caught by frontend-specific workflows
2. Frontend issues do not cause Python tests to fail while frontend tests pass
3. All workflows properly validate their respective areas of code

Fixes #5343

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:f985eb4-nikolaik   --name openhands-app-f985eb4   docker.all-hands.dev/all-hands-ai/openhands:f985eb4

[enyst]

Thank you so much for working on this, these workflows can be very annoying 😅