fix(cmd): close packetChan after capture goroutine finishes

- Add close(packetChan) after captureEngine.Run() completes
- Ensures packet processor goroutine exits cleanly when channel is drained
- Prevents potential goroutine leak during shutdown

Fixes potential resource leak identified in architecture audit

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

cmd/ja4sentinel/main.go

@@ -94,6 +94,7 @@ func main() {
 			"interface": appConfig.Core.Interface,
 		})
 		err := captureEngine.Run(appConfig.Core, packetChan)
+		close(packetChan) // Close channel to signal packet processor to shut down
 		captureErrChan <- err
 	}()