docs(bf-68f9i): document selected unmapped glyphs for test fixture
Created comprehensive glyph selection document for unmapped glyph test fixture.
Selected 4 unmapped glyph examples:
- PUA glyphs: /g001, /g002, /g003
- Custom encoding: /CustomA, /CustomB
- Orphaned codes: /NotAGlyph
- Non-AGL algorithmic: /glyph_0041
Selected 4 mapped AGL glyphs for comparison:
- /A, /B, /space (direct AGL entries)
- /uni0041 (algorithmic pattern)
Explained why each unmapped glyph fails all 4 mapping levels and provided
recommended fixture structure with expected output.
Closes bf-68f9i