Add an R smoke test using the example data

[eneskemalergin]

Summary

The repository includes example inputs, but there is no automated check confirming that the R filtering workflow still runs correctly.

Tasks

• add a lightweight smoke test that runs the R CLI on the example files
• assert that the expected output file is created
• assert that the output contains rows

Acceptance criteria

• the R example workflow can be checked with one command
• the test fails if the script stops producing a valid output file

Why this matters

This gives basic regression protection for the R implementation.