Fix DoubleFHT header and add ImageJ attribution to both FHT and GaussianBlur

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>

src/main/java/com/elphel/imagej/common/DoubleFHT.java

@@ -2,14 +2,16 @@ package com.elphel.imagej.common;
 
 /**
  **
- ** DoubleFHT - Determine simulation pattern parameters to match
- ** the acquired image
+ ** DoubleFHT.java - Fast Hartley Transform operating on double-precision arrays
+ **
+ ** Based on ImageJ FHT.java by Wayne Rasband, NIH (public domain).
+ ** Ported to double[] arrays for improved performance on modern hardware.
  **
  ** Copyright (C) 2010-2011 Elphel, Inc.
  **
  ** -----------------------------------------------------------------------------**
  **
- **  MatchSimulatedPattern.java is free software: you can redistribute it and/or modify
+ **  DoubleFHT.java is free software: you can redistribute it and/or modify
  **  it under the terms of the GNU General Public License as published by
  **  the Free Software Foundation, either version 3 of the License, or
  **  (at your option) any later version.

src/main/java/com/elphel/imagej/common/DoubleGaussianBlur.java

@@ -2,6 +2,9 @@
  **
  ** DoubleGaussianBlur.java - Gaussian blur for double-precision floating-point arrays
  **
+ ** Based on ImageJ GaussianBlur.java by Wayne Rasband, NIH (public domain).
+ ** Converted from float[] to double[], with additional methods.
+ **
  ** Copyright (C) 2014-2025 Elphel, Inc.
  **
  ** -----------------------------------------------------------------------------**