Add Polish (pl-PL) localization — checking conventions before starting

[majevva]

Summary

I would like to contribute a Polish (pl-PL) localization, starting with a small scout PR and scaling up incrementally by domain, following the pattern used for German (#1980) and Ukrainian (docs/uk-UA).

Context

• Existing locales: docs/zh-CN, docs/zh-TW, docs/ja-JP, docs/ko-KR, docs/pt-BR, docs/ru, docs/tr, docs/vi-VN, docs/th, docs/de-DE, docs/es, docs/uk-UA, docs/ur.
• CONTRIBUTING.md ("Cross-Harness and Translations") recommends opening an issue before translation work.
• I checked for an existing open/closed issue or PR for Polish and found none.
• I understand Add German (de-DE) localization — checking conventions before starting #1980's outcome: German followed a scout-PR-first plan (root docs/de-DE/README.md + GLOSSARY.md + installer registration), and incremental domain PRs afterward. I also saw that two parallel Spanish PRs (docs(es): add end-user Spanish documentation #2089, docs: add Spanish (es) translation #2095) had to be consolidated because they overlapped — I want to avoid duplicating effort, so I'm confirming here first.

Proposed plan

1. Scout PR (small, low risk): docs/pl-PL/README.md — full Polish translation of the current root README.md, following the docs/de-DE/README.md structure (not a new root README.pl-PL.md, since that pattern is legacy per your guidance in Add German (de-DE) localization — checking conventions before starting #1980). Add docs/pl-PL/GLOSSARY.md modeled on docs/ja-JP/GLOSSARY.md, deciding which ECC terms stay English (Agent, Skill, Hook, Command, Rule, Harness, Instinct, Plugin, Marketplace, Worktree, Subagent, Frontmatter) vs. take Polish forms.
2. Update the language selector tables in the root README and all existing localized READMEs so Polish is discoverable.
3. If installer registration should be part of the same PR (as it was for German), I'll add:
   • docs-pl-pl module in manifests/install-modules.json
   • locale:pl-pl component in manifests/install-components.json
   • pl-PL plus a pl alias in scripts/lib/install-manifests.js
   • focused coverage in tests/lib/locale-install.test.js
4. If accepted: incremental follow-up PRs by domain (commands/ → agents/ → rules/ → skills/) rather than one large localization PR, per the guidance already given for German.

Questions for maintainers

1. Is Polish wanted, and is pl-PL the right locale code (matching the de-DE / ja-JP style)?
2. Should installer registration ship in the same scout PR (as with German), or as a follow-up?
3. Any update-cadence expectations beyond "best effort" and stating the English source commit + scope, as already documented for German?

Happy to start on the scout PR as soon as this is confirmed. Thanks for maintaining such a clear contribution process.

[majevva]

One correction while awaiting your reply: on reflection I'll target docs/pl/README.md (short code pl) rather than pl-PL, matching the convention already used by docs/es, docs/ru, docs/tr, docs/th, and docs/ur — Polish doesn't need a region tag to disambiguate the way pt-BR/zh-CN/zh-TW do. Happy to switch to pl-PL instead if you'd rather match the de-DE/uk-UA/ja-JP/ko-KR region-tagged style for new additions — let me know either way. Starting the scout translation locally now; will hold the PR until you confirm scope/code.