Skip already-processed ZIPs by sampling first JPEG comment

Extracts one JPEG from each ZIP to check for the processing comment
before doing a full extract/resize/rezip cycle. Shared constants moved
to config.sh as single source of truth. Trap and cleanup extended to
cover the sample temp file.

images_resize.sh

@@ -5,10 +5,10 @@
 #
 # Usage: xxx.sh
 
-echo "Resizing large JPGs in $(pwd)"
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/config.sh"
 
-MAX_PIXELS=8000000
-MAGICK_COMMENT="magick:resize=8mp,quality=85,sampling=4:2:0"
+echo "Resizing large JPGs in $(pwd)"
 
 find . -regextype posix-egrep -regex ".*\.(jpg|JPG|JPEG|jpeg)$" -print0 | while IFS= read -r -d '' f
 do