Dynamic placement: below for instrumental, above for vocal-with-text

Dynamics sit below the staff for instrumental parts; for a vocal line with underlaid text, dynamics go above the staff so they are not confused with syllables placed below.

A chorale-tenor voice line carries both `lyric` and `dynamic` on the same note; the renderer places the dynamic below the staff regardless, where it collides with the lyric syllable directly beneath.

Gould, Behind Bars, ch. Dynamics ("vocal music: dynamics above the staff" — cited by chapter, not by an unverified page number); Ross, The Art of Music Engraving, ch. Dynamic Markings, gives the same split.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.