Upgrade guides now pair guide.md with guide.zh.md and guide.i18n.yaml under
the ordinary translation-pairing gate. verify-upgrade-guides checks the
Chinese sibling's metadata and its 变更/迁移 sections; the 500-word ceiling
applies to the English source. Remove the session-log-otel-collector guide.
Introduce docs/upgrade-guide/v<version>/<item>/guide.md for externally
perceptible breaking changes. The dsh-create-upgrade-guide skill owns scope,
placement, maintenance, and format; verify-upgrade-guides enforces layout,
frontmatter, sections, and the 500-word ceiling. Guides are English-only and
registered as the upgrade-guide document kind.
turtle1999