Concert-pitch score labeling

When a score for a transposing ensemble is presented at concert (sounding) pitch rather than each instrument's written pitch, the score must be explicitly labeled 'Score in C' / 'Concert pitch' — universal across Gould/Read/Ross since the two presentations are visually identical except key signature and octave placement, with no other cue.

Given score-transposing-instruments is presently a no-op, this cannot yet manifest as a content fault — flagged as a MODEL GAP to implement alongside it.

Gould (Behind Bars); standard publishing convention echoed by Ross.

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