Wire Twist Gene Pools into web calculator; simulate fold-sampling for 90% coverage

[micah-olivas]

Summary

• Twist Gene Pools synthesis cost: for sequences > 350 bp the calculator was using $0 for synthesis (no method was wired up). Now uses Twist Gene Pools lookup pricing (300–1800 bp, skew=1.5), so the uSort-M curve for long libraries reflects real synthesis costs.
• Simulation-based fold-sampling: the generator now calls find_fold_sampling() once per synthesis method at startup to find the fold required for 90% coverage, matching what usortm estimate does. Results: 8.5× for Twist Oligo Pools (skew=4.0) and 6.0× for Twist Gene Pools (skew=1.5). Previously hardcoded at 4×.
• UI updates: fold-sampling and skew labels below the plot now update dynamically from the JSON data; the synthesis method label for >500 bp now says "Twist Gene Pools (300–1800 bp)"; footnote assumptions updated for long libraries.
• TOML skew updates: Gene Pools 6.0→1.5, Cloned MGF 3.0→2.0, Multiplexed GF 5.0→2.0.
• All 29 cost curve JSONs and default_costs.json regenerated.

Test plan

• Open docs/index.html locally and verify the plot renders for 300 bp (short) and 700 bp (long)
• Confirm the "Fold sampling" and "Library skew" params below the plot update correctly when changing sequence length across the 350 bp threshold
• Confirm ">500 bp" synthesis label reads "Twist Gene Pools (300–1800 bp)"
• Confirm uSort-M cost at 700 bp / 1000 variants is non-zero and competitive with traditional