docs: center README project metrics

[erickkkyt]

What changed

• centers the full project-metrics table, not only its cell values
• applies the same layout to English, Chinese, and Japanese READMEs
• adds validation for the centered table structure

Repository description

Updated the GitHub About copy to: "A curated, source-reviewed gallery of JEV projects, tools, and open models—showing where JEV chooses, scores, routes, or filters, with fixed-commit evidence."

Verification

• npm test
• git diff --check