feat(ui): 服务器工具栏新增删除按钮

- 工具栏次序：新建服务器、新建分组、删除、分享；删除钮作用于当前
  选中节点，确认弹窗与右键菜单共用 deleteTarget 流（档位见
  deleteFacts）。
- 无选中、选择失效或选中项不可删除时禁用；资格判定新增政策缝
  CatalogWorkflow.canDelete（节点存在且 manual），订阅节点结构只读
  不经此口径，订阅删除仍留在订阅分区。
- CONTEXT.md Vocabulary 增补 Deletable node 术语；新增 canDelete
  接口测试。

CONTEXT.md

@@ -12,6 +12,7 @@
 - **Manual group**: A configuration group owned by the user. It may contain only manually owned nodes; deleting it recursively deletes its descendants. Deletion is always user-confirmed: one confirmation for an empty manual group, and a second confirmation naming the recursive subtree scale when it is non-empty.
 - **Subscription**: A remote configuration source with a persistent opaque UUID and a fixed subscription-group identity. Its URL is a mutable endpoint/credential reference; editing the URL keeps the source identity, while deleting and creating a subscription establishes a new source identity.
 - **Subscription group**: The fixed, source-owned configuration subtree provided by one subscription. Users cannot move or structurally edit its nodes. A subscription server's user-visible name is one remote-derived value from `remarks`, falling back to its address and port when absent, empty, or whitespace-only; each refresh derives that name from the latest remote record. It has no local alias or note override.
+- **Deletable node**: A manually owned node — a server configuration or a manual group — that the user can delete from the catalog. Subscription groups and their remote members are structurally read-only and are not deletable nodes; removing a subscription is subscription management, distinct from node deletion. _Avoid_: removable node.
 - **Active target**: The persisted server configuration or configuration group selected for proxying. When a group is active, the group UUID remains the target even when `sslocal` chooses an individual descendant server.
 - **Activation candidate**: A server configuration with no known local blocking problem for proxy configuration generation. This status does not guarantee remote reachability or correctness of opaque plugin options.
 - **Managed plugin**: A SIP003 plugin executable that the product packages, hash-verifies, re-signs, and distributes only inside the app bundle. The managed set changes only with app releases; users cannot supply their own plugin executables.

ShadowsocksX-NG2/App/CatalogWorkflow/CatalogWorkflow+Policy.swift

@@ -6,6 +6,14 @@ import Foundation
 extension CatalogWorkflow {
   // MARK: - 删除确认事实
 
+  /// 删除资格（命令入口的统一 disable 判据，如分区工具栏删除钮）：节点存在
+  /// 且来源为 manual。订阅节点结构只读（CONTEXT.md），其移除属订阅分区流程，
+  /// 不经此口径。
+  func canDelete(_ id: NodeID) -> Bool {
+    guard let node = tree.node(withID: id) else { return false }
+    return node.isManual
+  }
+
   /// 删除确认档位（CONTEXT.md：空手动组/服务器单次；非空手动组二次并点名规模）。
   /// 节点不存在时为 `nil`。
   func deleteFacts(for id: NodeID) -> DeleteConfirmKind? {

ShadowsocksX-NG2/App/ServersView.swift

@@ -265,6 +265,19 @@ extension ServersView {
       .labelStyle(.iconOnly)
       .help("新建分组")
     }
+    // 删除：作用于当前选中的服务器叶子或手动分组，确认弹窗与右键菜单共用
+    // deleteTarget 流（档位见 deleteFacts）；无选中或选中项不可删（订阅节点
+    // 结构只读，CONTEXT.md）即禁用，资格判定归政策 seam。
+    ToolbarItem(placement: .primaryAction) {
+      Button {
+        deleteTarget = selection
+      } label: {
+        Label("删除", systemImage: "trash")
+      }
+      .labelStyle(.iconOnly)
+      .help("删除")
+      .disabled(!canDeleteSelection)
+    }
     // 分享（分享/导出术语见 CONTEXT.md）：作用于选中的服务器叶子，弹窗内
     // 提供二维码与复制 ss:// 链接两条通路；无有效载荷即不可用。
     ToolbarItem(placement: .primaryAction) {
@@ -288,6 +301,11 @@ extension ServersView {
 
   // MARK: - 告警动作
 
+  /// 工具栏删除钮可用性：无选中或选中项不可删（订阅节点、失效选择）即禁用。
+  private var canDeleteSelection: Bool {
+    selection.map(workflow.canDelete) ?? false
+  }
+
   private func presentNewGroup(in parent: NodeID?) {
     newGroupParent = parent
     newGroupName = ""

ShadowsocksX-NG2/Tests/CatalogWorkflowPolicyTests.swift

@@ -79,6 +79,22 @@ final class CatalogWorkflowPolicyTests: XCTestCase {
       .subtree(count: 3, includesCredentials: true))
   }
 
+  // MARK: - 删除资格
+
+  func testCanDeleteManualLeafAndGroupButNotSubscriptionOrMissing() async throws {
+    let serverID = try await importServer()
+    let groupID = try await workflow.createGroup(named: "组", into: nil)
+    XCTAssertTrue(workflow.canDelete(serverID), "手动叶子可删")
+    XCTAssertTrue(workflow.canDelete(groupID), "手动分组可删（空组同理）")
+
+    let fixture = try CatalogFixtures.makeSubscriptionFixture()
+    try CatalogFileStore(fileURL: fileURL).save(CatalogDocument(catalog: fixture.catalog))
+    workflow = makeWorkflow()
+    XCTAssertFalse(workflow.canDelete(fixture.serverIDs[0]), "订阅成员结构只读")
+    XCTAssertFalse(workflow.canDelete(fixture.groupID), "订阅分组结构只读")
+    XCTAssertFalse(workflow.canDelete(NodeID(rawValue: "ghost")), "节点不存在")
+  }
+
   // MARK: - 移动目的地
 
   func testMoveDestinationsAreRootAndManualGroupsExcludingOwnSubtree() async throws {