Frequency Rank speed training

25/25 correct; first Frequency Rank PB 11.437s→4.823s. Reuse: one left-to-right scan with six counters kept in lexical slot order (amber,birch,cinder,drift,ember,frost); select top 3 by count, preserving slot order on ties, then emit immediately. Inferring frost as a residual was slower. Bottleneck: 24-token scan + runtime variance.