feat: add Windows UDP broadcast relay (#2222)

This may helps games to find rooms in virtual network.

- add opt-in Windows UDP broadcast relay config flag and CLI/env plumbing
- capture local UDP broadcasts with Windows raw sockets, normalize packets, and inject them via PeerManager

easytier-web/frontend-lib/src/components/Config.vue

@@ -99,6 +99,7 @@ const bool_flags: BoolFlag[] = [
   { field: 'disable_encryption', help: 'disable_encryption_help' },
   { field: 'disable_tcp_hole_punching', help: 'disable_tcp_hole_punching_help' },
   { field: 'disable_udp_hole_punching', help: 'disable_udp_hole_punching_help' },
+  { field: 'enable_udp_broadcast_relay', help: 'enable_udp_broadcast_relay_help' },
   { field: 'disable_upnp', help: 'disable_upnp_help' },
   { field: 'disable_sym_hole_punching', help: 'disable_sym_hole_punching_help' },
   { field: 'enable_magic_dns', help: 'enable_magic_dns_help' },

easytier-web/frontend-lib/src/locales/cn.yaml

@@ -160,6 +160,9 @@ disable_tcp_hole_punching_help: 禁用TCP打洞功能
 disable_udp_hole_punching: 禁用UDP打洞
 disable_udp_hole_punching_help: 禁用UDP打洞功能
 
+enable_udp_broadcast_relay: UDP 广播中继
+enable_udp_broadcast_relay_help: "仅 Windows：捕获物理网卡上的本机 UDP 广播包并转发给 EasyTier 对等节点，帮助局域网游戏发现房间。需要管理员权限。"
+
 disable_upnp: 禁用 UPnP
 disable_upnp_help: 禁用符合条件监听器的运行时 UPnP/NAT-PMP 端口映射；自动端口映射默认开启。
 
@@ -260,6 +263,7 @@ event:
   DhcpIpv4Conflicted: DHCP IPv4地址冲突
   PortForwardAdded: 端口转发添加
   ProxyCidrsUpdated: 子网代理CIDR更新
+  UdpBroadcastRelayStartResult: UDP广播中继启动结果
 
 web:
   login:

easytier-web/frontend-lib/src/locales/en.yaml

@@ -159,6 +159,9 @@ disable_tcp_hole_punching_help: Disable tcp hole punching
 disable_udp_hole_punching: Disable UDP Hole Punching
 disable_udp_hole_punching_help: Disable udp hole punching
 
+enable_udp_broadcast_relay: UDP Broadcast Relay
+enable_udp_broadcast_relay_help: "Windows only: capture local UDP broadcast packets from physical interfaces and forward them to EasyTier peers. Helps games to find rooms in local network. Requires administrator privileges."
+
 disable_upnp: Disable UPnP
 disable_upnp_help: Disable runtime UPnP/NAT-PMP port mapping for eligible listeners; automatic port mapping is enabled by default.
 
@@ -260,6 +263,7 @@ event:
   DhcpIpv4Conflicted: DhcpIpv4Conflicted
   PortForwardAdded: PortForwardAdded
   ProxyCidrsUpdated: ProxyCidrsUpdated
+  UdpBroadcastRelayStartResult: UDP Broadcast Relay Start Result
 
 web:
   login:

easytier-web/frontend-lib/src/types/network.ts

@@ -134,6 +134,7 @@ export interface NetworkConfig {
   disable_tcp_hole_punching?: boolean
   disable_udp_hole_punching?: boolean
   disable_upnp?: boolean
+  enable_udp_broadcast_relay?: boolean
   disable_sym_hole_punching?: boolean
 
   enable_relay_network_whitelist?: boolean
@@ -211,6 +212,7 @@ export function DEFAULT_NETWORK_CONFIG(): NetworkConfig {
     disable_tcp_hole_punching: false,
     disable_udp_hole_punching: false,
     disable_upnp: false,
+    enable_udp_broadcast_relay: false,
     disable_sym_hole_punching: false,
     enable_relay_network_whitelist: false,
     relay_network_whitelist: [],
@@ -447,4 +449,6 @@ export enum EventType {
   PortForwardAdded = 'PortForwardAdded', // PortForwardConfigPb
 
   ProxyCidrsUpdated = 'ProxyCidrsUpdated', // string[], string[]
+
+  UdpBroadcastRelayStartResult = 'UdpBroadcastRelayStartResult', // { capture_backend?: string, error?: string }
 }