fix: POC 扫描接入调用方 context，修复 cachedPocPath 竞争和 ProxyStats data race

- webscan/web_scan.go: WebScan 接受 ctx 参数，替换 context.Background()；
  sync.Once 改为 sync.Mutex 保护 POC 加载，消除 cachedPocPath 并发写竞争
- webtitle.go: ctx 从 Scan 穿透到 identifyFingerprintsMulti → triggerPocScan → WebScan
- webpoc.go: 传递 ctx 到 WebScan
- proxy/types.go: ProxyStats 增加 sync.Mutex
- proxy/manager.go: LastConnectTime/LastError/AverageConnectTime 读写加锁

common/proxy/manager.go

@@ -264,11 +264,16 @@ func (d *directDialer) DialContext(ctx context.Context, network, address string)
 	conn, err := dialer.DialContext(ctx, network, address)
 
 	duration := time.Since(start)
+
+	d.stats.mu.Lock()
 	d.stats.LastConnectTime = start
+	d.stats.mu.Unlock()
 
 	if err != nil {
 		atomic.AddInt64(&d.stats.FailedConnections, 1)
+		d.stats.mu.Lock()
 		d.stats.LastError = err.Error()
+		d.stats.mu.Unlock()
 		return nil, NewProxyError(ErrTypeConnection, ErrMsgDirectConnFailed, ErrCodeDirectConnFailed, err)
 	}
 
@@ -323,15 +328,22 @@ func (s *socks5Dialer) DialContext(ctx context.Context, network, address string)
 	select {
 	case <-dialCtx.Done():
 		atomic.AddInt64(&s.stats.FailedConnections, 1)
+		s.stats.mu.Lock()
 		s.stats.LastError = dialCtx.Err().Error()
+		s.stats.mu.Unlock()
 		return nil, NewProxyError(ErrTypeTimeout, ErrMsgSOCKS5ConnTimeout, ErrCodeSOCKS5ConnTimeout, dialCtx.Err())
 	case result := <-connChan:
 		duration := time.Since(start)
+
+		s.stats.mu.Lock()
 		s.stats.LastConnectTime = start
+		s.stats.mu.Unlock()
 
 		if result.err != nil {
 			atomic.AddInt64(&s.stats.FailedConnections, 1)
+			s.stats.mu.Lock()
 			s.stats.LastError = result.err.Error()
+			s.stats.mu.Unlock()
 			return nil, NewProxyError(ErrTypeConnection, ErrMsgSOCKS5ConnFailed, ErrCodeSOCKS5ConnFailed, result.err)
 		}
 
@@ -347,7 +359,8 @@ func (s *socks5Dialer) DialContext(ctx context.Context, network, address string)
 
 // updateAverageConnectTime 更新平均连接时间
 func (d *directDialer) updateAverageConnectTime(duration time.Duration) {
-	// 简单的移动平均
+	d.stats.mu.Lock()
+	defer d.stats.mu.Unlock()
 	if d.stats.AverageConnectTime == 0 {
 		d.stats.AverageConnectTime = duration
 	} else {
@@ -356,7 +369,8 @@ func (d *directDialer) updateAverageConnectTime(duration time.Duration) {
 }
 
 func (s *socks5Dialer) updateAverageConnectTime(duration time.Duration) {
-	// 简单的移动平均
+	s.stats.mu.Lock()
+	defer s.stats.mu.Unlock()
 	if s.stats.AverageConnectTime == 0 {
 		s.stats.AverageConnectTime = duration
 	} else {

common/proxy/types.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/tls"
 	"net"
+	"sync"
 	"time"
 )
 
@@ -95,9 +96,10 @@ type ProxyManager interface {
 //
 //nolint:revive // 保持与现有代码的向后兼容性
 type ProxyStats struct {
-	TotalConnections   int64         `json:"total_connections"`
-	ActiveConnections  int64         `json:"active_connections"`
-	FailedConnections  int64         `json:"failed_connections"`
+	TotalConnections   int64  `json:"total_connections"`
+	ActiveConnections  int64  `json:"active_connections"`
+	FailedConnections  int64  `json:"failed_connections"`
+	mu                 sync.Mutex    `json:"-"`
 	AverageConnectTime time.Duration `json:"average_connect_time"`
 	LastConnectTime    time.Time     `json:"last_connect_time"`
 	LastError          string        `json:"last_error,omitempty"`