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

cmd/webui4frpc/main.go

@@ -568,8 +568,9 @@ func retryRejoinCached(ctx context.Context, ring *cluster.Engine, peersJSON stri
 }
 
 // reachableAddr returns an address peers can dial back: an explicit
-// W4F_HOST (compose DNS name) wins; otherwise a non-wildcard listen addr; a
-// wildcard falls back to the hostname (routable inside docker networks).
+// W4F_HOST (compose DNS name) wins; otherwise a non-wildcard listen addr;
+// a wildcard falls back to the primary non-loopback IPv4 detected from the
+// interfaces (routable on plain LAN hosts); hostname is the last resort.
 func reachableAddr(addr string) string {
 	if h := os.Getenv("W4F_HOST"); h != "" {
 		if _, port, err := net.SplitHostPort(addr); err == nil {
@@ -582,6 +583,9 @@ func reachableAddr(addr string) string {
 		return addr
 	}
 	if host == "" || host == "0.0.0.0" || host == "::" || host == "[::]" {
+		if ip := primaryLANIPv4(); ip != "" {
+			return net.JoinHostPort(ip, port)
+		}
 		if h, herr := os.Hostname(); herr == nil && h != "" {
 			return net.JoinHostPort(h, port)
 		}
@@ -589,6 +593,31 @@ func reachableAddr(addr string) string {
 	return addr
 }
 
+// primaryLANIPv4 returns the first global-scope non-loopback IPv4 address of
+// any up interface, preferring RFC1918 ranges. Empty string when none found.
+func primaryLANIPv4() string {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return ""
+	}
+	var fallback string
+	for _, a := range addrs {
+		ipnet, ok := a.(*net.IPNet)
+		if !ok || ipnet.IP.To4() == nil || ipnet.IP.IsLoopback() || !ipnet.IP.IsGlobalUnicast() {
+			continue
+		}
+		ip := ipnet.IP.To4()
+		if fallback == "" {
+			fallback = ip.String()
+		}
+		// prefer private ranges over link-local / unusual globals
+		if ip[0] == 10 || (ip[0] == 172 && ip[1]&0xf0 == 16) || (ip[0] == 192 && ip[1] == 168) {
+			return ip.String()
+		}
+	}
+	return fallback
+}
+
 // splitCSV splits a comma-separated list into a slice (empty -> nil).
 func splitCSV(s string) []string {
 	if strings.TrimSpace(s) == "" {