Refine project overview and runtime documentation

[ChanTso]

Clarify client, agent, and transaction responsibilities across the English and Chinese project overviews and runtime guide. Simplify fixture and evaluation terminology while keeping commands, links, and recorded results intact.

Validation:

• git diff --check passed.
• All 69 relative documentation links in the changed files resolve locally.
• Independent documentation review passed.
• Documentation-only changes; no application tests or measurements were rerun locally. The normal CI matrix runs on this PR.