DoubleFHT.java had a copy-paste error in its GPL header (wrong description
and wrong filename from MatchSimulatedPattern). Fixed both and added
attribution to the ImageJ FHT.java source (Wayne Rasband, NIH, public domain).

DoubleGaussianBlur.java already had an in-class attribution comment; added
a matching note in the GPL header for consistency.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>