feat: 重构侧边栏布局，当前账号移至底部卡片并支持快速切换，下载任务独立为顶级菜单

apps/macos/VODManager/Sources/VODManager/Views/ContentView.swift

@@ -22,8 +22,10 @@ struct ContentView: View {
 
 struct SidebarView: View {
     @EnvironmentObject var accountStore: AccountStore
+    @State private var showAccountPicker = false
 
     var body: some View {
+        VStack(spacing: 0) {
             List {
                 Section("媒体库") {
                     NavigationLink(destination: VideoListView()) {
@@ -31,26 +33,66 @@ struct SidebarView: View {
                     }
                 }
 
+                Section("下载") {
+                    NavigationLink(destination: DownloadTaskListView()) {
+                        Label("下载任务", systemImage: "arrow.down.circle")
+                    }
+                }
+
                 Section("管理") {
                     NavigationLink(destination: AccountListView()) {
                         Label("账号配置", systemImage: "key")
                     }
-                NavigationLink(destination: DownloadTaskListView()) {
-                    Label("下载任务", systemImage: "arrow.down.circle")
-                }
                     NavigationLink(destination: LogListView()) {
                         Label("操作日志", systemImage: "doc.text")
                     }
                 }
+            }
 
             if let account = accountStore.activeAccount {
-                Section("当前账号") {
+                Divider()
-                    Label(account.name, systemImage: "checkmark.circle.fill")
+                VStack(spacing: 8) {
+                    HStack {
+                        Image(systemName: "checkmark.circle.fill")
                             .foregroundStyle(.green)
+                        Text(account.name)
+                            .font(.headline)
+                            .lineLimit(1)
+                        Spacer()
+                    }
+                    HStack {
                         Text(account.region)
                             .font(.caption)
                             .foregroundStyle(.secondary)
+                        Spacer()
                     }
+
+                    if accountStore.accounts.count > 1 {
+                        Menu {
+                            ForEach(accountStore.accounts) { acct in
+                                Button {
+                                    Task { await accountStore.switchActive(acct) }
+                                } label: {
+                                    HStack {
+                                        Text(acct.name)
+                                        if acct.id == account.id {
+                                            Image(systemName: "checkmark")
+                                        }
+                                    }
+                                }
+                            }
+                        } label: {
+                            Label("切换账号", systemImage: "arrow.triangle.2.circlepath")
+                                .font(.caption)
+                        }
+                        .buttonStyle(.bordered)
+                        .controlSize(.small)
+                    }
+                }
+                .padding(12)
+                .background(.quaternary.opacity(0.5), in: RoundedRectangle(cornerRadius: 10))
+                .padding(.horizontal, 8)
+                .padding(.bottom, 8)
             }
         }
         .navigationTitle("火炬VOD管理器")