- Add Glyph struct with 10 fields per plan spec (Phase 3.2)
- Implement emit_glyph() that composes Glyph from GraphicsState + font metrics
- Add new_raw_glyph_list() helper with 4096 capacity pre-allocation
- Use Box<Color> to optimize struct size to 64 bytes
- Add comprehensive tests for all acceptance criteria
- Re-export Glyph, emit_glyph, new_raw_glyph_list from lib.rs
Closes: pdftract-4j0ub
