docs: add earned OpenSSF passing badge

[rare]

Summary

• add the official OpenSSF Best Practices badge for project 13940
• update readiness documentation to the awarded Passing state and preserve the public-repository-only scope
• replace the pre-award validation guard with an official passing-status evidence guard

Verification

• official project page reports 100% Passing
• OpenSSF assessment validator: 67 unique criteria
• 13 Node tests passed
• publish Action fixture passed
• Claude, Cursor, and Gemini package validators passed
• workflow pin validation passed
• live npm release checksum verification passed for CLI 0.1.3 and MCP 0.1.0