feat: SDK agent integration + UDP plugin framework + SNMP plugin

SDK enhancements for endpoint agent embedding:
- ScanWithController for pause/resume and live stats
- OnProgress callback for periodic progress reporting
- TaskID injection into every scan result
- ScanController with goroutine-safe pause/resume/stats
- Multi-target stats aggregation (race-free)

UDP plugin infrastructure:
- PluginTypeUDP registry with dedicated dispatch path
- DialUDP on ScanSession with rate limiting and packet counting
- UDP plugins bypass TCP port scan, probe targets directly
- FilterService excludes UDP plugins from TCP port matching

SNMP plugin (first UDP plugin):
- SNMPv2c GetRequest probe for sysDescr detection
- Community string brute force (public/private/community/etc)
- Pure stdlib implementation (encoding/asn1)
- Registered as safe default plugin on port 161/UDP

Tests: 95.7% SDK coverage, race-free, 50+ new test cases

core/base_scan_strategy.go

@@ -106,6 +106,10 @@ func (b *BaseScanStrategy) isLocalPlugin(pluginName string) bool {
 	return plugins.HasType(pluginName, plugins.PluginTypeLocal)
 }
 
+func (b *BaseScanStrategy) isUDPPlugin(pluginName string) bool {
+	return plugins.IsUDP(pluginName)
+}
+
 func (b *BaseScanStrategy) isLocalPluginExplicitlySpecified(pluginName string, config *common.Config) bool {
 	return config.LocalPlugin == pluginName
 }
@@ -141,6 +145,11 @@ func (b *BaseScanStrategy) isPluginApplicableToPort(pluginName string, targetPor
 
 // isPluginPassesFilterType 检查插件是否通过过滤器类型检查
 func (b *BaseScanStrategy) isPluginPassesFilterType(pluginName string, isCustomMode bool, config *common.Config) bool {
+	// UDP 插件有独立分发路径，不参与 TCP 端口匹配流水线
+	if b.isUDPPlugin(pluginName) {
+		return false
+	}
+
 	// 自定义模式下强制运行所有明确指定的插件
 	if isCustomMode {
 		return true
@@ -155,8 +164,8 @@ func (b *BaseScanStrategy) isPluginPassesFilterType(pluginName string, isCustomM
 		}
 		return false
 	case FilterService:
-		// 服务扫描策略：排除本地插件
-		return !b.isLocalPlugin(pluginName)
+		// 服务扫描策略：排除本地插件和UDP插件（UDP有独立分发路径）
+		return !b.isLocalPlugin(pluginName) && !b.isUDPPlugin(pluginName)
 	case FilterWeb:
 		// Web扫描策略：只允许Web插件
 		return b.isWebPlugin(pluginName)
@@ -231,9 +240,9 @@ func (b *BaseScanStrategy) getPluginsByFilterType() []string {
 			}
 		}
 	case FilterService:
-		// 服务扫描策略：排除本地插件和纯Web插件，保留服务插件
+		// 服务扫描策略：排除本地插件和UDP插件，保留TCP服务插件
 		for _, pluginName := range allPlugins {
-			if !b.isLocalPlugin(pluginName) {
+			if !b.isLocalPlugin(pluginName) && !b.isUDPPlugin(pluginName) {
 				filteredPlugins = append(filteredPlugins, pluginName)
 			}
 		}

core/scanner.go

@@ -211,6 +211,12 @@ func ExecuteScanTasks(ctx context.Context, session *common.ScanSession, targets
 		default:
 		}
 
+		if session.PauseGate != nil {
+			if err := session.PauseGate(ctx); err != nil {
+				return
+			}
+		}
+
 		targetPort := target.Port
 
 		for _, pluginName := range pluginsToRun {
@@ -262,6 +268,12 @@ func executeScanTask(ctx context.Context, session *common.ScanSession, pluginNam
 	default:
 	}
 
+	if session.PauseGate != nil {
+		if err := session.PauseGate(ctx); err != nil {
+			return
+		}
+	}
+
 	// 长驻插件不进 WaitGroup，通过 ctx 管理生命周期
 	if longRunningPlugins[pluginName] {
 		ready := make(chan struct{}, 1)

core/service_scanner.go

@@ -10,6 +10,7 @@ import (
 	"github.com/shadow1ng/fscan/common"
 	"github.com/shadow1ng/fscan/common/i18n"
 	"github.com/shadow1ng/fscan/common/parsers"
+	"github.com/shadow1ng/fscan/plugins"
 )
 
 // ServiceScanStrategy 服务扫描策略
@@ -161,6 +162,11 @@ func (s *ServiceScanStrategy) performHostScan(ctx context.Context, session *comm
 		return
 	}
 
+	// UDP 插件并行分发：直接对存活主机发协议探测包，不走端口扫描
+	if len(hosts) > 0 {
+		s.dispatchUDPPlugins(ctx, session, hosts, info, config, ch, wg)
+	}
+
 	// 流式 channel：端口扫描发现开放端口后立即通知插件执行
 	stream := make(chan string, 64)
 
@@ -213,6 +219,34 @@ func (s *ServiceScanStrategy) performHostScan(ctx context.Context, session *comm
 	}
 }
 
+// dispatchUDPPlugins 分发UDP协议插件，跳过TCP端口扫描链路
+func (s *ServiceScanStrategy) dispatchUDPPlugins(ctx context.Context, session *common.ScanSession, hosts []string, baseInfo common.HostInfo, config *common.Config, ch chan struct{}, wg *sync.WaitGroup) {
+	allPlugins, isCustomMode := s.GetPlugins(config)
+
+	var udpPlugins []string
+	for _, name := range allPlugins {
+		if plugins.IsUDP(name) {
+			if isCustomMode || plugins.IsSafe(name) {
+				udpPlugins = append(udpPlugins, name)
+			}
+		}
+	}
+	if len(udpPlugins) == 0 {
+		return
+	}
+
+	for _, host := range hosts {
+		for _, pluginName := range udpPlugins {
+			for _, port := range plugins.GetPluginPorts(pluginName) {
+				target := baseInfo
+				target.Host = host
+				target.Port = port
+				executeScanTask(ctx, session, pluginName, target, ch, wg)
+			}
+		}
+	}
+}
+
 // PrepareTargets 准备目标信息
 func (s *ServiceScanStrategy) PrepareTargets(info common.HostInfo, session *common.ScanSession) []common.HostInfo {
 	// 发现目标主机和端口