chore: strip ui/, docs/, and app/site CI from core

Removes the Electron app and website from this repo as part of the
multi-repo split:

- git rm -r ui/        (now in leifericf/noumenon-app)
- git rm -r docs/      (now in leifericf/noumenon-site, plus 4
                        internal design plans preserved only in
                        this repo's history)
- ci.yml: drop the ui job (shadow-cljs build)
- release.yml: drop build-electron and deploy-pages jobs; drop
  pages: write and id-token: write from permissions
- README.md: link Visual UI section to leifericf/noumenon-app
- DEVELOPMENT.md: remove ui/ and docs/ from project layout, add
  cross-links to the two split repos

The full pipeline left in core's release.yml is build-jar +
build-launcher + integration-test + release + docker +
update-homebrew + update-scoop. CLI distribution tokens
(HOMEBREW_TAP_TOKEN, SCOOP_BUCKET_TOKEN) stay here.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: leifericf