feat(frpLogger): add real-time instance log streaming functionality

Implement cross-platform log streaming for frpc instances with support for Windows, systemd, and init.d systems. Includes WebSocket API endpoint for real-time log streaming, token validation, and instance ownership checks. Update README and API documentation to reflect new functionality.

The implementation handles:
- Platform-specific log collection (Windows Event Log, journalctl, log files)
- WebSocket-based real-time streaming
- Token validation and instance access control
- Log level parsing and formatting
- Historical log retrieval since service start

frpLogger/os.go

@@ -0,0 +1,65 @@
+package frpLogger
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"runtime"
+	"strings"
+)
+
+func GetInitSystem() string {
+	if runtime.GOOS == "windows" {
+		return "windows"
+	}
+	if runtime.GOOS == "linux" {
+		if _, err := os.Stat("/run/systemd/system"); err == nil {
+			return "systemd"
+		}
+		if _, err := os.Stat("/etc/init.d"); err == nil {
+			return "init.d"
+		}
+	}
+	return "unknown"
+}
+
+func IsInstanceRunning(instanceID int) bool {
+	initType := GetInitSystem()
+	serviceName, err := GetServiceNameByInstanceID(instanceID)
+	if err != nil {
+		return false
+	}
+
+	switch initType {
+	case "windows":
+		cmd := exec.Command("sc", "query", serviceName)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			return false
+		}
+		return strings.Contains(string(output), "RUNNING")
+
+	case "systemd":
+		cmd := exec.Command("systemctl", "is-active", serviceName)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			return false
+		}
+		return strings.TrimSpace(string(output)) == "active"
+
+	case "init.d":
+		servicePath := fmt.Sprintf("/etc/init.d/%s", serviceName)
+		if _, err := os.Stat(servicePath); err != nil {
+			return false
+		}
+		cmd := exec.Command(servicePath, "status")
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			return false
+		}
+		return strings.Contains(string(output), "is running")
+
+	default:
+		return false
+	}
+}