fix(desktop): 设置窗口透明化 + 自绘 MacWindow 框，去掉原生白边（12A 实测反馈）

Overlay 标题栏模式下原生 NSWindow 底色在深色内容四周露出白边。改为
与托盘菜单一致的模式：窗口 transparent + shadow:false，由页面自绘
窗框（对齐原型 MacWindow 规格：radius-md + border-1 + shadow-window，
16px 阴影边距，窗口尺寸相应 472x592），红绿灯 trafficLightPosition
对齐自绘顶条，内容区独立滚动。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

desktop/src-tauri/Cargo.toml

@@ -12,7 +12,7 @@ crate-type = ["staticlib", "cdylib", "rlib"]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
-tauri = { version = "2", features = ["tray-icon"] }
+tauri = { version = "2", features = ["macos-private-api", "tray-icon"] }
 tauri-plugin-global-shortcut = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"

desktop/src-tauri/tauri.conf.json

@@ -15,12 +15,18 @@
         "label": "settings",
         "title": "dudu 设置",
         "url": "index.html",
-        "width": 440,
-        "height": 560,
+        "width": 472,
+        "height": 592,
         "resizable": false,
         "visible": false,
         "titleBarStyle": "Overlay",
-        "hiddenTitle": true
+        "hiddenTitle": true,
+        "transparent": true,
+        "shadow": false,
+        "trafficLightPosition": {
+          "x": 30,
+          "y": 28
+        }
       },
       {
         "label": "overlay",