Add Catalan translation guidelines for Airflow UI

[DonthaNagaTarun]

This PR adds Catalan (ca) translation guidelines for the Airflow UI
under .github/skills/airflow-translations/locales/ca.md.

The document describes:

• Which Airflow terms should remain untranslated
• Preferred translations for UI-specific terms
• Consistency guidelines for translators

This helps improve translation quality and maintain consistency
across the Airflow UI.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide (https://github.com/apache/airflow/blob/main/contributing-docs/README.rst)
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it's a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
• Always keep your Pull Requests rebased, otherwise your build might fail due to changes not related to your commits.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: dev@airflow.apache.org
  Slack: https://s.apache.org/airflow-slack

[DonthaNagaTarun]

Happy to expand these guidelines to other locales if needed.

[potiuk]

cc: @ecodina @oscarhernandezrodriguez

[ecodina]

cc: @ecodina @oscarhernandezrodriguez

Yes! I read about it some days ago int he Devlist but hadn't had time to work on that. I'll try to review it this week to ensure it aligns with the current translations.

[DonthaNagaTarun]

Thanks a lot for taking the time to review this!
Please let me know if any changes or adjustments are needed from my side.