- voice_formulas.py: add pairs_to_formula() as canonical implementation
- webui/routes/utils/voice.py: formula_from_profile() and pairs_to_formula()
now delegate to voice_formulas.pairs_to_formula()
- pyqt/gui.py: get_voice_formula() now uses voice_formulas.pairs_to_formula()
instead of inline string formatting
- Eliminates 3 duplicate implementations of voice*weight formula building
- +9 tests
- 1178 tests pass
