English becomes the default · Chinese moves to /zh

English is now the site’s primary language: the root paths (/, /docs/**, /dev/**, /changelog) serve English directly, and Chinese moves entirely to /zh/** (/zh, /zh/docs/**, /zh/dev/**, /zh/changelog); the header’s EN / 中文 switch preserves the current path (/docs/overview ↔ /zh/docs/overview).

• Mechanism: the docs collection holds the English tree (Nimbus versions.current: "en"), and docs-zh is mounted at /zh via versions.others; the old /en/** routes and the docs-en collection are removed.
• Untranslated pages: spec / PRD / ADR in the English tree still show the Chinese source with This page has not been translated yet. at the top; the reverse case (an English page without Chinese) shows 本页暂未提供中文。 in the /zh tree. Neither notice can be dismissed.
• Generation: scripts/sync-docs.mjs now writes the Chinese repo sources into both trees (the English tree flags the fallback with untranslated, the Chinese tree stays clean); the English architecture page goes to the root tree, the Chinese one to the /zh tree.
• Metadata: the root llms.txt describes the English tree and links /zh/llms.txt; the root llms-full.txt is English; sitemap / canonical / markdown alternates / RSS are correct per tree; Pagefind still indexes both languages.