docs: add bilingual research notes

[minixalpha]

Summary

• Split research notes into hand-written Chinese sources under docs/research/zh-CN/ and generated English versions under docs/research/en/.
• Add complete English translations for the agent-tools, read-tool, write-tool, and edit-tool research notes.
• Route English and Chinese development notes to research in the matching language.
• Document the bilingual research workflow and make PR preparation report English translation status whenever a Chinese source changes.
• Start the 0.7.x changelog with this documentation change.

Validation

• uv run pytest — 76 passed
• Verified all local Markdown links.
• Verified matching heading levels, code fences, table rows, and external URLs across each bilingual research pair.