Add some utils to generate cards via imagemagick

sample_data/cards/generate_card.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+mkdir -p output
+
+for img in input/*.{jpg,png}; do
+  [ -e "$img" ] || continue  # skip if no files
+  name=$(basename "${img%.*}").jpg
+  magick convert background.png \
+    \( "$img" -resize x820 \) \
+    -gravity center -composite \
+    -quality 85 -sampling-factor 4:4:4 \
+    "output/$name"
+done