Fix contributor burst anomaly ranking

[rogerchappel]

Summary

• add adaptive per-user contribution burst adjustment for suspicious isolated daily spikes
• preserve raw public commit totals while ranking on adjusted commit signals only when a burst cap applies
• collect GitHub contribution calendar daily counts and validate optional burst metadata
• document the methodology and add a regression script for low-baseline vs high-volume cases

Validation

• pnpm run test:burst
• pnpm run check
• pnpm run validate:data
• pnpm run build