Add zero-change client catalog preview

[denial123789]

Summary

• surface catalog --json before the connection commands in all three READMEs
• let visitors verify the complete supported-client catalog without signing in or changing local files
• keep English, Chinese, and Japanese documentation aligned

Validation

• executed npm exec --yes --package=@sandbaseai/cli@0.1.14 -- sandbase catalog --json against the published package; it returned the 25-client catalog
• git diff --check
• npm run build
• npm run audit:package