Sync shared governance baseline

[hindermath]

Summary

• sync the shared governance, statistics, bilinguality, and accessibility baseline across the local guidance files
• align README and docs/README with the shared CEFR-B2, German-first, .EN.md, and DocFX A11Y rules
• add the final ## Gesamtstatistik block with ASCII diagrams to docs/project-statistics.md

Testing

• not run (documentation/governance-only change)