DMG 背景图: PIL 生成箭头 + 中文提示, 布局对齐

之前只有两个图标并排, 用户看不出来要拖拽. 现在在 DMG 挂载打开时:
- 中间一根灰箭头从 .app 指向 Applications
- 底部中文提示 "将左侧应用拖到右侧 Applications 即完成安装"
- 窗口/图标/箭头三者坐标对齐

实现:
- 用 PIL 在 staging 阶段生成 600x400 PNG, 放 .background/bg.png
  (dot 前缀让 Finder 默认隐藏)
- AppleScript 里 set background picture 用 HFS path (冒号分隔)
- 图标位置 {150,200} / {450,200} 与背景图箭头两端对齐

PIL 字体查找: PingFang (默认中文) -> STHeiti -> Helvetica -> 兜底,
在打包机上都会命中至少一个.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

@@ -92,12 +92,54 @@ TMP_DMG="dist/.tmp_rw.dmg"
 STAGE="dist/.dmg_stage"
 VOL_NAME="ZB100ImageGenerator"
 
-# 1. 准备 staging: .app + Applications 快捷方式
+# 1. 准备 staging: .app + Applications 快捷方式 + 背景图
 rm -rf "$STAGE"
-mkdir -p "$STAGE"
+mkdir -p "$STAGE/.background"
 cp -R "dist/ZB100ImageGenerator.app" "$STAGE/"
 ln -s /Applications "$STAGE/Applications"
 
+# 用 PIL 生成带箭头+中文提示的背景图 (600x400, 跟 DMG 窗口尺寸匹配)
+DMG_BG_PATH="$STAGE/.background/bg.png" python3 <<'PYEOF'
+import os
+from PIL import Image, ImageDraw, ImageFont
+
+W, H = 600, 400
+img = Image.new('RGB', (W, H), color=(248, 248, 250))
+d = ImageDraw.Draw(img)
+
+# 中间箭头 (从 .app 指向 Applications)
+arrow_y = 200
+arrow_color = (120, 120, 125)
+d.line([(260, arrow_y), (425, arrow_y)], fill=arrow_color, width=5)
+d.polygon(
+    [(425, arrow_y - 14), (455, arrow_y), (425, arrow_y + 14)],
+    fill=arrow_color,
+)
+
+# 底部提示文字
+def load_font(size):
+    for path in (
+        "/System/Library/Fonts/PingFang.ttc",
+        "/System/Library/Fonts/STHeiti Medium.ttc",
+        "/System/Library/Fonts/Helvetica.ttc",
+    ):
+        if os.path.exists(path):
+            try:
+                return ImageFont.truetype(path, size)
+            except Exception:
+                continue
+    return ImageFont.load_default()
+
+font = load_font(22)
+text = "将左侧应用拖到右侧 Applications 即完成安装"
+bbox = d.textbbox((0, 0), text, font=font)
+tw = bbox[2] - bbox[0]
+d.text(((W - tw) // 2, 320), text, fill=(90, 90, 95), font=font)
+
+img.save(os.environ['DMG_BG_PATH'])
+print(f"[dmg] 背景图已生成: {os.environ['DMG_BG_PATH']}")
+PYEOF
+
 # 2. 先卸载可能残留的同名卷, 防止上次失败留下的挂载
 hdiutil detach "/Volumes/$VOL_NAME" -force >/dev/null 2>&1 || true
 
@@ -121,12 +163,16 @@ tell application "Finder"
         set current view of container window to icon view
         set toolbar visible of container window to false
         set statusbar visible of container window to false
-        set the bounds of container window to {200, 120, 800, 470}
+        -- 窗口尺寸匹配背景图 600x400, 坐标系从屏幕左上角算
+        set the bounds of container window to {200, 120, 800, 520}
         set theViewOptions to the icon view options of container window
         set arrangement of theViewOptions to not arranged
         set icon size of theViewOptions to 128
-        set position of item "ZB100ImageGenerator.app" of container window to {160, 170}
-        set position of item "Applications" of container window to {440, 170}
+        -- 设置背景图 (HFS path, 冒号分隔)
+        set background picture of theViewOptions to file ".background:bg.png"
+        -- 图标位置要跟背景图里的箭头对齐
+        set position of item "ZB100ImageGenerator.app" of container window to {150, 200}
+        set position of item "Applications" of container window to {450, 200}
         update without registering applications
         delay 1
         close