fix: divide BBI by actual number of calc params

[NemeZZiZZ]

Problem

BBI averages its moving averages over a hard-coded 4 instead of the actual number of parameters:

const maxPeriod = Math.max(...params)   // derived from params
...
bbi.bbi = maSum / 4                      // ← fixed divisor

mas and maxPeriod both follow calcParams, but the divisor does not.

Verified by execution: calcParams: [3, 6, 12] on flat data at 100 yields 75 instead of 100; with 5 params the result is 25% low.

Impact

Any non-default calcParams silently produces wrong BBI values. Default [3, 6, 12, 24] is unaffected.

Fix

maSum / params.length, guarded against an empty calcParams (previously 0/4 = 0; keep 0 rather than NaN).

One line, one file.