Add Polish (pl_PL) translation - current app structure (4975 keys)

[MarioJack123]

Summary

Complete Polish (pl_PL) translation of Msty Studio.

Note on structure: this repo's en_US.json (3573 keys) is behind the version currently shipped in the Msty Studio app (4975 keys) — e.g. modelHub.localModels.huggingfaceModels.* has been reorganized into modelHub.localModels.modelSearch.*, and a few other keys were renamed. This pl_PL.json matches the current app structure (extracted from the app's own locale-template.json), so it has more keys than en_US.json in this repo right now. Structure/placeholders/@:-alias/ICU-plural parity was verified against the current app's en_US.json, not the one currently committed here. Happy to also open a PR updating en_US.json if that's useful — didn't want to touch it unprompted since the README notes it's maintained by the Msty team.

I also noticed there are two earlier open PRs for pl_PL (#14, #15) built against the older structure — not trying to step on either, just offering a version that matches what the app currently ships, in case it's useful for comparison or as a base.

Quality process

• Preserved all existing translated strings; did not blanket-retranslate.
• Fixed several outright mistranslations found during review, e.g. model → was "Modelka" (unrelated word meaning "female model"), search-provider brand names Brave/Exa/SearXNG that had been translated as ordinary words instead of left as product names, and "Hugging Face" translated literally as a body part ("przytulona twarz").
• Fixed grammar (case/gender agreement) in composed strings using @: linked references, where Polish declension didn't match the referenced nominative form.
• Aligned terminology with a glossary (Chat/Conversation → "Rozmowa" consistently; a few @:-composed spots needed "czat" instead, where the app treats Chat/Conversation/Forge Canvas as distinct convertible types).
• Verified: 0 missing/extra keys vs. current app template, 0 placeholder mismatches, 0 alias-token mismatches (except where intentionally resolved inline for grammar), 0 ICU/plural form-count mismatches, valid JSON/UTF-8, no duplicate keys.

Guidelines checklist

• Preserve JSON Structure (matches current app's en_US.json / template — see note above re: this repo's copy being outdated)
• Maintain Accuracy
• UTF-8 Encoding