fix: 完善同事未完成的修改 — LAN 地址检测/画布删除撤销/连线删除按钮/Del 键/注释修正

- cmd/webui4frpc/main.go: 新增 primaryLANIPv4() 检测内网 LAN 地址,
  解决三台内网主机间集群发现失败 (reachableAddr 只回退到 hostname)
- internal/httpapi/handlers.go: applyCanvas 新增拓扑差异检测,
  画布删除连线时自动 RevokeTask 避免集群残留
- web/src/api.ts: 新增 addLink / deleteLink API 封装
- web/src/components/PortEdge.vue: × 删除按钮移到端口标签右上角 (绝对定位)
- web/src/views/CanvasView.vue: 启用 Del/Backspace 键删除选中连线
  (确认对话框 + 走 onDeleteEdge 逻辑), 修正注释
- embed dist 同步

web/src/views/CanvasView.vue

@@ -65,6 +65,7 @@
             @label-drag="onLabelDrag"
             @toggle-disabled="onToggleDisabled"
             @edit-group="onEditGroup"
+            @delete-edge="onDeleteEdge"
           />
         </template>
       </VueFlow>
@@ -466,6 +467,61 @@ const editEdge = (edge: Edge) => {
   )
 }
 
+// onDeleteEdge removes an edge from the canvas after a confirm dialog.
+// The removed link is persisted on the next save: applyCanvas (PUT /canvas)
+// replaces links wholesale and revokes any cluster task for links that
+// disappeared. The × badge on the edge label is the quick entry; the
+// Delete/Backspace key (keydown handler below) removes SELECTED edges.
+const onDeleteEdge = async ({ edgeId }: { edgeId: string }) => {
+  const e = edges.value.find((x) => x.id === edgeId)
+  if (!e) return
+  try {
+    await ElMessageBox.confirm('确认删除该连线？删除后需点击「保存配置」生效。', '删除连线', {
+      confirmButtonText: '删除',
+      cancelButtonText: '取消',
+      type: 'warning',
+    })
+  } catch {
+    return // cancelled
+  }
+  removeEdgesSilently([edgeId])
+}
+
+// onCanvasKeydown handles Delete/Backspace to drop all SELECTED edges after a
+// single shared confirmation (VueFlow's own delete-key handling stays disabled
+// via :delete-key-code="null" because we must keep removal behind the same
+// confirm dialog; nodes have their own delete buttons).
+const onCanvasKeydown = async (ev: KeyboardEvent) => {
+  if (ev.key !== 'Delete' && ev.key !== 'Backspace') return
+  const tag = (ev.target as HTMLElement | null)?.tagName
+  if (tag === 'INPUT' || tag === 'TEXTAREA' || tag === 'SELECT') return
+  if (!canWrite.value) return
+  const selectedIds = edges.value
+    .filter((x): x is Edge & { selected?: boolean } => Boolean((x as Edge & { selected?: boolean }).selected))
+    .map((x) => x.id)
+  if (selectedIds.length === 0) return
+  ev.preventDefault()
+  try {
+    await ElMessageBox.confirm(
+      `确认删除选中的 ${selectedIds.length} 条连线？删除后需点击「保存配置」生效。`,
+      '删除连线',
+      { confirmButtonText: '删除', cancelButtonText: '取消', type: 'warning' },
+    )
+  } catch {
+    return // cancelled
+  }
+  removeEdgesSilently(selectedIds)
+}
+
+// removeEdgesSilently drops the given edge ids from the canvas without its own
+// prompt (the callers already confirmed). Marks the canvas dirty.
+const removeEdgesSilently = (ids: string[]) => {
+  const gone = new Set(ids)
+  edges.value = edges.value.filter((x) => !gone.has(x.id))
+  assignLayers()
+  dirty.value = true
+}
+
 // onEdgeLabelClick finds the edge by id and opens its port editor.
 const onEdgeLabelClick = ({ edgeId }: { edgeId: string }) => {
   const e = edges.value.find((x) => x.id === edgeId)
@@ -815,8 +871,10 @@ onMounted(() => {
     attributes: true,
     attributeFilter: ['data-theme'],
   })
+  window.addEventListener('keydown', onCanvasKeydown)
 })
 onBeforeUnmount(() => {
+  window.removeEventListener('keydown', onCanvasKeydown)
   themeObserver?.disconnect()
   themeObserver = null
 })