Added more robust DBH estimation through the how argument. The original ITSMe behaviour can be obtained with how = "mean"; how = "median" (new default) uses the median point-to-centre radius; and numeric values use a trimmed mean of the point-to-centre radii.
Updated the lower-trunk fallback logic in dbh_pc() so that a well-supported direct DBH slice is less likely to be overwritten because of noisy or incomplete lower-stem points.
Documented the new DBH estimation options and quality-control metrics in the main ITSMe vignette.