docs: link Documentation to the homepage and redraw the workflow diagram

[qiansc]

Summary

• The README Documentation link (and 文档 in README.zh-CN) opens the homepage at https://context4ai.org/.
• Redraw the How it works diagram in the documentation site style: sources feed production and updates, all three workflows (production, updates, retrieval) cross one body of reviewed knowledge, outputs reach agents, bots and people, and the evidence chain leads back to the original at a pinned commit. English and Chinese versions share one layout.

Validation

• Rendered both SVGs with rsvg-convert and checked the layout.

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