fix(example): explicit FILE_EXT in config_exp_psfex.ini

Same latent FILE_PATTERN/FILE_EXT length mismatch 3eb6a66 fixed
elsewhere: the 3-entry FILE_PATTERN override fell back on the
decorator's new 4-entry FILE_EXT default, tripping the length check
at startup.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: cailmdaley

example/cfis/config_exp_psfex.ini

@@ -64,6 +64,10 @@ INPUT_DIR = last:split_exp_runner, last:mask_runner
 # Read pipeline flag files created by mask module
 FILE_PATTERN = image, weight, pipeline_flag
 
+# Explicit extensions: a 3-entry FILE_PATTERN override must not fall back on
+# the decorator's 4-entry FILE_EXT default (length check fails at startup)
+FILE_EXT = .fits, .fits, .fits
+
 NUMBERING_SCHEME = -0000000-0
 
 # SExtractor executable path