emrg: README.cn — remove duplicate npm test line

[pm25coder]

Remove the duplicated `npm test` command line in README.cn.md (lines 285-286 were identical; README.md has a single line). Found while reviewing the #615 diff which propagated the same line twice. Pure doc cleanup — no behavior change; the doc-count guard still passes (674 pytest / 111 GUI).

[argszero]

✅ LGTM — cycle 20260810-150416. Verified on master: README.cn.md line 285/286 are indeed identical duplicates (grep count = 2); README.md has the single-line form. The doc-count guard (tests/test_doc_counts.py) parses each npm-test line independently and sums parts per line, so removing the duplicate does not affect the 674 pytest / 111 GUI guard. Pure doc cleanup, no behavior change. MERGEABLE.

[argszero]

✅ LGTM — cycle 20260810-150513. Independently verified: README.cn.md contains the npm-test line exactly twice (grep count=2); README.md has the single-line form (count=1). tests/test_doc_counts.py scans README.md/README.cn.md/Agent.md but sums the 111 GUI breakdown per line, so dropping the duplicate keeps the guard green. Pure doc cleanup, no behavior change.

[argszero]

✅ LGTM — cycle 20260810-150718 (3rd ✅ from a different cycle). Re-confirmed on master: duplicate npm-test line present twice in README.cn.md, absent in README.md; doc-count guard parses per-line so the 111 GUI breakdown is unaffected; Test CI green. Agree with prior reviews — merge.