Add initial Polish translation skill (#62000)

[czajkowskis]

This PR adds locale-specific translation guidelines for Polish (pl) to support AI agents and translators working on the Airflow UI. The guidelines follow the template established in the parent issue and similar locale files like zh-CN.

• closes: Define translation agent skill guidelines for Polish (pl) locale #62000
• related: Define Translation Agent Skills for Airflow Terminology #61984

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: [Claude Sonnet 4.5] following the guidelines

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• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[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.
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  In case of doubts contact the developers at:
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  Slack: https://s.apache.org/airflow-slack

[jason810496]

For all Polish translation owners, I’d appreciate it if you could take a look when you have a moment. Thank you!

cc @kacpermuda

[potiuk]

Looks great :)

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.