docs(zh-cn): complete missing translations and localize ecosystem sidebar (#2355)

Add Chinese translations for the two remaining untranslated docs
(named-agents, expand-bmad-for-your-org) and add i18n translations
for the BMad Ecosystem sidebar group and its items across all locales.

Co-authored-by: leon <leon.liang@hairobotics.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>