docs(rfc): profile dashboard and exact handoff Markdown export

[Zxf-xufeng]

Which issue or RFC does this PR close?

Design source: Dashboard补齐制品（RFC）.

Rationale for this change

Dashboard already provides Prompts and Topic Memory on master. The remaining gap is a read-only Profile page and downloading the exact Handoff revision selected by the user.

What changes are included in this PR?

• Synchronized English and Chinese RFCs covering Profile content, revision history, evidence, exact Handoff Markdown, directory return state, and authentication recovery.
• Four UI pre-design images: Profile, Handoff collection, detail, and mobile reading.
• Document generation support for repository-relative RFC images so the same sources render on GitHub and the documentation site.

Are there any user-facing changes?

Design documentation only. The proposal preserves existing Prompts and Topic Memory behavior, existing public APIs, and the current Dashboard authentication boundary.

How was this change tested?

• make check
• uv run prek run -a
• make docs-test: verified 808 exported public pages and local assets.
• Reviewed both locale documents and all four UI pre-design images.

AI usage statement

Prepared and validated with OpenAI Codex, including drafting, implementation exploration, and automated checks. Maintainer review is requested through this draft PR.