feat(client/macos): 开机自启用 SMAppService + LoginItem helper(学 Tailscale)

根因:launch_at_startup 0.5.1 在 macOS 无自带实现,需宿主接 MethodChannel,而我们 Runner
从没实现 → enable() 抛 MissingPluginException 被 try/catch 吞掉 → 登录项从未注册,自启失败。
学 Tailscale(LoginItemHelper-macsys + SMAppService):
- 新增无界面 LoginItem helper(macos/login_helper,LSBackgroundOnly),登录时带 --autostart
  拉起主 app(→隐藏到托盘);
- build_login_helper.sh 构建期编译+签名+嵌入 Contents/Library/LoginItems/(新 Run Script 阶段);
- MainFlutterWindow 接 launch_at_startup MethodChannel → SMAppService.loginItem 注册/注销。
构建通过:helper 嵌入+签名,主 app --deep --strict 校验过。Windows 自启(schtasks)不变。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/macos/Runner/MainFlutterWindow.swift

@@ -1,7 +1,12 @@
 import Cocoa
 import FlutterMacOS
+import ServiceManagement
 
 class MainFlutterWindow: NSWindow {
+  // launch_at_startup 插件在 macOS 没自带实现,需宿主接 MethodChannel。学 Tailscale 用
+  // SMAppService.loginItem 注册内置的 PangolinLoginHelper(登录时它带 --autostart 拉起主 app)。
+  private let loginHelperID = "com.pangolin.pangolin.LoginHelper"
+
   override func awakeFromNib() {
     let flutterViewController = FlutterViewController()
     self.contentViewController = flutterViewController
@@ -18,6 +23,9 @@ class MainFlutterWindow: NSWindow {
     // 需 VpnChannel.swift 已加入 Runner target 的 Compile Sources。
     VpnChannel.register(with: flutterViewController.registrar(forPlugin: "VpnChannel"))
 
+    // 开机自启 MethodChannel(launch_at_startup 插件的原生侧,macOS 需宿主实现)。
+    registerLaunchAtStartupChannel(messenger: flutterViewController.engine.binaryMessenger)
+
     super.awakeFromNib()
 
     // 开机自启(登录项带 --autostart):不弹主窗口,直接隐藏到托盘(与 Windows 一致)。
@@ -27,4 +35,36 @@ class MainFlutterWindow: NSWindow {
       self.orderOut(nil)
     }
   }
+
+  // launch_at_startup 的 macOS 原生实现:SMAppService.loginItem 注册/注销 LoginHelper。
+  private func registerLaunchAtStartupChannel(messenger: FlutterBinaryMessenger) {
+    let channel = FlutterMethodChannel(name: "launch_at_startup", binaryMessenger: messenger)
+    let helperID = loginHelperID
+    channel.setMethodCallHandler { call, result in
+      guard #available(macOS 13.0, *) else {
+        result(FlutterError(code: "unsupported", message: "开机自启需 macOS 13+", details: nil))
+        return
+      }
+      let svc = SMAppService.loginItem(identifier: helperID)
+      switch call.method {
+      case "launchAtStartupIsEnabled":
+        result(svc.status == .enabled)
+      case "launchAtStartupSetEnabled":
+        let on = ((call.arguments as? [String: Any])?["setEnabledValue"] as? Bool) ?? false
+        do {
+          if on {
+            if svc.status != .enabled { try svc.register() }
+          } else {
+            if svc.status == .enabled { try svc.unregister() }
+          }
+          result(nil)
+        } catch {
+          NSLog("[pangolin/launch] SMAppService %@ failed: %@", on ? "register" : "unregister", error.localizedDescription)
+          result(FlutterError(code: "smappservice", message: error.localizedDescription, details: nil))
+        }
+      default:
+        result(FlutterMethodNotImplemented)
+      }
+    }
+  }
 }