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

README.md

@@ -52,6 +52,7 @@
 - **并发控制** - 端口扫描线程、服务扫描线程独立配置
 
 ### 扩展功能
+- **SDK嵌入** - `pkg/fscan`提供Go SDK，可嵌入Agent或安全平台，支持任务控制(Pause/Resume)、实时进度回调、TaskID追溯
 - **Web管理界面** - 可视化扫描任务管理(条件编译 -tags web)
 - **Lab靶场环境** - 内置Docker靶场用于测试学习
 - **插件化架构** - 服务插件/Web插件/本地插件分离，易于扩展
@@ -234,6 +235,11 @@ yay -S fscan-git
 - **后两周** - Bug修复与代码整合
 - **欢迎PR** - 期待您的贡献！
 
+### SDK & Agent 集成
+- 扩展SDK能力，完善端侧Agent嵌入支持
+- 断点续扫、带宽级限速、内存水位控制
+- 更多Agent场景的集成示例
+
 ### 插件生态
 - 持续扩展服务插件覆盖范围
 - 为每个服务插件开发更多漏洞检测和利用能力