cb54637e9f
Phase 2 (refactor-commit-12..18) created Controls/ with 6 UserControls that split MainWindow.xaml, but no index.md existed — a gap against the schema.md rule (one index.md per code directory). Documents each control, the window↔ control contract, and the Phase-2 landmines (window-resources converter rule, control xmlns, name-looked-up host stubs, dropped-Border).