Generators can now have independent step counts. When merging patterns
of different lengths, both are tiled to their LCM. Chain exposes
setGeneratorStepCount/getGeneratorStepCount for polyrhythmic control.
Replace the pitch*127 encoding hack with a dedicated midiNote field on
pattern steps. IntervalLock now writes integer MIDI notes to step.midiNote
while preserving the original [0,1] pitch for other consumers. The clock
and sequencer bridge pass midiNote through the event pipeline.
Also reworks mergePatterns to be trigger-aware: when only one generator
fires at a step, use its values directly instead of averaging with the
other generator's defaults.
