docs: correct strict ecosystem growth target

[LauraGPT]

Summary

Correct the campaign's strict "more than 20,000 additional stars" boundary: baseline 31,224 requires at least 51,225, not 51,224. Update the English introduction/metric, Chinese summary, and the dated September 5 snapshot's gap (14,061).

Document --target-additional-stars 20001 for the existing inclusive collector. Historical measurement dates, collector defaults/API, runtime code, releases, and deployment remain unchanged.

Type of change

• Documentation
• Bug fix

Validation

• Three new documentation checks failed against the original document, including 51224 != 51225.
• Candidate: 94 tests passed across growth-target, existing growth-plan, collector, and roadmap suites.
• actionlint 1.7.12 and git diff --check passed.
• GitHub GFM render checked for corrected threshold and collector option.
• Independent read-only review found no P1/P2 findings.
• Existing exact-head roadmap workflow now runs the new dependency-free contract.

User impact

Prevents equating reaching +20,000 with exceeding it. This is a documentation correction, not evidence of new stars or campaign completion.

Notes for reviewers

No runtime changes, PyPI release, production deployment, or issue closure.