chore(docs): split business/strategy docs out of the public repo

[pftg]

The repo is public, which is right for what it mostly is: the site, the theme, the test suite, and the engineering knowledge in .okf/. Those are a credibility asset and should stay open.

docs/business/ and the 20-29-strategy/ sections under docs/projects/*/ are a different category. They are internal planning artifacts - commercial positioning, offer design, project bets, capacity and scheduling notes. They are not useful to a visitor to this repo and do not need to be here.

Proposal

Move the business layer to a private repo (or a private submodule), leaving the public repo with:

• content/, themes/, layouts/, assets/, test/, bin/
• .okf/ engineering knowledge bundle
• The Johnny Decimal engineering areas under docs/ (10-19 core dev, 20-29 testing, 30-39 architecture, 50-59 deployment, 80-89 integration)
• docs/workflows/ cross-cutting pipeline how-tos
• docs/adr/, docs/incidents/, docs/design-system/

Open questions for Paul

1. Private repo vs private submodule vs a non-git home.
2. Migrate history for the moved paths, or start the private repo fresh at the current tip.
3. Where CLAUDE.md pointers should resolve to afterwards - several @docs/... references in CLAUDE.md and the blog pipeline point at strategy files that would move.

Notes

• ~455 files are tracked under docs/ today; this affects the business subset only.
• This is an org decision, not a mechanical refactor. Not something to action autonomously.