[Enhancement] Improve and complete Polish (pl) translations

[wlzukowski]

Currently, the Polish (pl) language support in Hi.Events is incomplete, and the quality of the existing translations is quite poor and unnatural in some places.

I would like to contribute by doing a comprehensive review and rewrite of the Polish translation to ensure it sounds natural. I will also translate the currently untranslated strings to provide a complete experience for Polish users.

My plan is to:

• Update the backend translation files.

• Update the frontend translation files using Lingui.

As per the contribution guidelines, I am opening this issue first to get alignment before starting the work and submitting a PR.

[daveearley]

Thanks for the offer, @wlzukowski! We'd happily accept improvements to the translations.