Update RPi scripts and docs for v4.2.0

- Default branch: 4.1 → 4.2
- Update prebuilt URL to v4.2.0
- Update example filenames to 4.2.0
- Remove jpegio references (now using jpeglib)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/pull-image.sh

@@ -3,7 +3,7 @@
 # Resizes rootfs to 16GB for consistent image size, then pulls
 #
 # Usage: ./pull-image.sh <device> <output.img.zst>
-# Example: ./pull-image.sh /dev/sdb stegasoo-rpi-4.1.5.img.zst
+# Example: ./pull-image.sh /dev/sdb stegasoo-rpi-4.2.0.img.zst
 
 set -e
 
@@ -15,7 +15,7 @@ NC='\033[0m'
 
 if [ $# -ne 2 ]; then
     echo "Usage: $0 <device> <output.img.zst>"
-    echo "Example: $0 /dev/sdb stegasoo-rpi-4.1.5.img.zst"
+    echo "Example: $0 /dev/sdb stegasoo-rpi-4.2.0.img.zst"
     exit 1
 fi