v2.6.7 — Documentation: GEO/SEO + first tagged release

First tagged release of Auto-Claude-Chinese. Internal package.json was at 2.6.6 from upstream-sync work but no git tag existed before — this codifies v2.6.7 as a stable pinnable baseline. Adds llms.txt (AI search engine index), bilingual SEO keyword block, README nav row. Behavior, prompts, pipeline, and CLI surface unchanged. Upstream: AndyMik90/Auto-Claude.