Update Polish locale

[tamtejszystan]

Summary

This PR improves the Polish locale in src/i18n/locales/pl.yaml.

Changes

• Fixed typos and minor grammar issues.
• Improved several sentences to sound more natural and fluent in Polish.
• Replaced some awkward or overly literal wording with clearer phrasing.
• Removed minor punctuation and formatting errors, such as unnecessary semicolons or stray characters.

Checks

• python3 lint_yaml.py
• npm run build
• npm run validate

Thanks for the initiative. I'm glad I could contribute, even in a small way ;)

[marcprux]

Thanks! Please verify that it looks OK: https://keepandroidopen.org/pl/