Added typed config struct for unmapped glyph names configuration:
- unmapped_glyph_names: Vec<String> - list of glyph names to skip
- description: Option<String> - optional documentation
- version: Option<String> - format version identifier
The struct represents the JSON structure from build/unmapped-glyph-names.json
and is ready for parsing implementation in follow-up beads.
Closes bf-3vo80. Verification: notes/bf-3vo80.md
2ba56d8186