Hairpin minimum length

A hairpin needs enough horizontal room to read as a wedge rather than an accent mark (`>`). CORRECTED FROM DRAFT: neither Gould nor Ross states a specific numeric minimum span in beats — Ross's guidance (The Art of Music Engraving, ch. Dynamic Markings) is qualitative ("a hairpin must be long enough to be legible as a gradual change, not confused with an accent"), not a beat count. The 1.0-beat floor below is a Gradus engineering heuristic modeled on that qualitative guidance, not a cited numeric authority rule, and should be labeled as such in any user-facing message.

`hairpins: [{ from: 10, to: 11, type: "cresc" }]` spanning two sixteenth notes — at normal spacing this wedge is only a few pixels wide and reads as a stray accent mark, not a crescendo.

Ross, The Art of Music Engraving, ch. Dynamic Markings — qualitative minimum-length guidance only, no specific number given; Gould shows only hairpins spanning several notes in her examples but likewise gives no numeric floor. The 1.0-beat threshold is a Gradus-authored heuristic, not a direct citation.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.