refactor(ui): 订阅与诊断分区自持错误弹窗,塌缩两个 destination 包装壳

SubscriptionsView/DiagnosticsView 改为自持 ErrorAlertPresenter 并经
presentingErrors 挂载(与 ServersView 同法),只为转发 presenter 而存在的
WorkspaceSubscriptionsView/WorkspaceDiagnosticsView 整体删除,窗口壳
destinationView 直挂分区视图;WorkspaceHomeView 因承载旧版导入主动弹窗
保留。穿透链 13 个类型减至 11 个,presenter owner 减至 3 个。

ShadowsocksX-NG2/App/DiagnosticsView.swift

@@ -8,7 +8,8 @@ import SwiftUI
 /// 的唯一 UI-facing seam）；本视图只负责生命周期触发、呈现与复制动作。
 struct DiagnosticsView: View {
   @ObservedObject var diagnostics: DiagnosticsWorkflow
-  let errors: ErrorAlertPresenter
+  /// 共享错误弹窗呈现（UI 持有；typed error → 本地化文案的呈现边缘）。
+  @StateObject private var errors = ErrorAlertPresenter()
   let clipboard: any TextClipboard
 
   enum LogSource: String, CaseIterable, Identifiable {
@@ -49,6 +50,7 @@ struct DiagnosticsView: View {
       .padding(.bottom, 36)
     }
     .task { await diagnostics.readWhileActive() }
+    .presentingErrors(errors)
   }
 
   // MARK: - 状态摘要

ShadowsocksX-NG2/App/MainWindowView.swift

@@ -211,7 +211,7 @@ struct MainWindowView: View {
         clipboard: clipboard,
         configurationGroupFileExporter: configurationGroupFileExporter)
     case .subscriptions:
-      WorkspaceSubscriptionsView(
+      SubscriptionsView(
         workflow: workflow,
         onNodesRemoved: clearSelectionIfInvalidated)
     case .rules:
@@ -225,7 +225,7 @@ struct MainWindowView: View {
       )
       .frame(maxWidth: .infinity, maxHeight: .infinity)
     case .diagnostics:
-      WorkspaceDiagnosticsView(
+      DiagnosticsView(
         diagnostics: diagnostics,
         clipboard: clipboard)
     }

ShadowsocksX-NG2/App/SubscriptionsView.swift

@@ -7,7 +7,8 @@ import SwiftUI
 /// （非敏感）；结构化刷新状态在呈现层本地化（story 42）。
 struct SubscriptionsView: View {
   @ObservedObject var workflow: CatalogWorkflow
-  let errors: ErrorAlertPresenter
+  /// 共享错误弹窗呈现（UI 持有；typed error → 本地化文案的呈现边缘）。
+  @StateObject private var errors = ErrorAlertPresenter()
   /// 删除完成后回调（被删身份集合；主窗口据此清除失效选择）。
   let onNodesRemoved: (Set<NodeID>) -> Void
 
@@ -60,6 +61,7 @@ struct SubscriptionsView: View {
         "将移除订阅源、固定分组与全部远端成员；若代理正走此订阅，代理会停止。此操作不可撤销。"
       )
     }
+    .presentingErrors(errors)
   }
 
   private func commitDelete() {

ShadowsocksX-NG2/App/WorkspaceDestinations.swift

@@ -1,7 +1,8 @@
 import SwiftUI
 
-/// 主窗口各 destination 的包装视图（票 #53/#54）：负责每个分区的共享
-/// alert/sheet 生命周期，行为委托给既有分区视图。
+/// 首页 destination 的包装视图：承载旧版导入主动弹窗与共享错误弹窗挂载
+/// （票 #53/#54），行为委托给 HomeView。订阅/诊断分区自持错误弹窗（与
+/// ServersView 同法），不再需要包装。
 
 struct WorkspaceHomeView: View {
   @ObservedObject var workflow: CatalogWorkflow
@@ -34,34 +35,3 @@ struct WorkspaceHomeView: View {
     .presentingErrors(errors)
   }
 }
-
-struct WorkspaceSubscriptionsView: View {
-  @ObservedObject var workflow: CatalogWorkflow
-  let onNodesRemoved: (Set<NodeID>) -> Void
-  @StateObject private var errors = ErrorAlertPresenter()
-
-  var body: some View {
-    SubscriptionsView(
-      workflow: workflow,
-      errors: errors,
-      onNodesRemoved: onNodesRemoved
-    )
-    .presentingErrors(errors)
-  }
-}
-
-struct WorkspaceDiagnosticsView: View {
-  @ObservedObject var diagnostics: DiagnosticsWorkflow
-  let clipboard: any TextClipboard
-  @StateObject private var errors = ErrorAlertPresenter()
-
-  var body: some View {
-    // 导出诊断动作在窗口工具栏（票 #58）；本包装只承载复制错误呈现。
-    DiagnosticsView(
-      diagnostics: diagnostics,
-      errors: errors,
-      clipboard: clipboard
-    )
-    .presentingErrors(errors)
-  }
-}