- README.md is now English; add README.zh-CN.md with cross-links; both versions
cover the same 40 sections and the same key facts
- correct stale docs/design.md 10.5.1 and docs/todo.md to the current code
(XAUTOCLAIM threshold, malformed-entry ACK, error envelope now done)
- replace the temporary HANDOFF.md with docs/todo.md (unfinished work + blockers)
- adjust docs/deployment.md and AGENTS.md accordingly
