docs(readme): restore curated Markdown README

The merge race landed the other agent auto-converted README (asciidoctor
artifacts, still said 115 cartridges, kept the dead Green-Hosting badge,
lost the SonarCloud badge). Restore the hand-written version: accurate
125/68/0.4.7, honest catalogue-vs-live framing, SonarCloud quality-gate
badge, dead Green-Hosting badge removed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath