- Add notes/bf-e4uvb-child-1.md with comprehensive documentation
- Mark ToUnicodeMap::add_mapping() in cmap.rs (line 86)
- Mark DifferencesOverlay entry creation in encoding.rs (line 195)
- Mark CodespaceRange creation in codespace.rs (line 256)
These are the critical insertion points for future unmapped glyph skip logic.
Closes bf-e4uvb-child-1.
