Reorganize the DevMap testing guide

[itsflaid]

Summary

• reorganize the private testing guide around the actual DevMap artifacts being tested
• document fast source testing without a build or reinstall
• document local dist, external tarball, npm exec, and npm link workflows
• add step-by-step Groq live testing, expected results, reinstall guidance, and cleanup
• retain automated, error recovery, cross-version, CI, and web testing instructions

Validation

• source CLI --version and --help
• production dist build, --version, and --help
• balanced Markdown code fences
• stale test-count and secret-pattern scan
• git diff --check