ci: add universal macOS release workflow

scripts/create-mac-icon.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+project_root="$(cd "$(dirname "$0")/.." && pwd)"
+source_icon="$project_root/resources/icon.png"
+iconset="$project_root/build/icon.iconset"
+output="$project_root/build/icon.icns"
+
+mkdir -p "$iconset"
+for size in 16 32 128 256 512; do
+  sips -z "$size" "$size" "$source_icon" --out "$iconset/icon_${size}x${size}.png" >/dev/null
+  retina=$((size * 2))
+  sips -z "$retina" "$retina" "$source_icon" --out "$iconset/icon_${size}x${size}@2x.png" >/dev/null
+done
+iconutil -c icns "$iconset" -o "$output"
+echo "Created $output"
+