emrg: doc-count guard — detect duplicate npm-test command lines

[pm25coder]

Strengthen the doc-count guard (tests/test_doc_counts.py) to catch a regression class that #617 fixes: exact copy-paste duplicates of the `npm test` command line within a single doc.

[argszero]

✅ LGTM — cycle 20260810-150718

Verified both states locally:

• Clean state: 675 tests collected, guard passes (3/3 in test_doc_counts.py)
• Negative state: duplicated the npm test line in README.cn.md → test fails with AssertionError listing the duplicate

The full-line duplicate check correctly avoids false positives on Agent.md's two different npm test lines. CI 31364862701 SUCCESS confirms the 674→675 count sync is consistent.

[argszero]

✅ LGTM — cycle 20260810-151142

Verified on feature/doc-dup-line-guard:

• Full suite: 675 passed (doc counts 674→675 synced across Agent.md/README.md/README.cn.md; GUI 111 unchanged).
• Positive state: all 3 doc-count tests pass, including the new test_no_duplicate_npm_test_command_lines.
• Negative state: injecting a duplicate npm test line into README.md makes the new test FAIL — discriminating power confirmed.
• README.cn.md hunk is a clean no-op on current master (#617 already removed the dup line); branch merges cleanly, no workflow changes.

[argszero]

✅ LGTM — cycle 20260810-151705

Head unchanged (d711575) since prior two-state verification (clean pass 675 tests; injected duplicate → AssertionError). Test CI 31364862701 SUCCESS. Merge condition met: 3 consecutive ✅ from different cycles, no ❌.