refactor(util): move panel version comparison into a shared package

The node-assignment path in the service package needs the same
MAJOR.MINOR.PATCH comparison the panel updater uses, but service/panel
imports service, so the helper cannot stay there.

internal/util/version/version.go

@@ -0,0 +1,47 @@
+// Package version compares 3x-ui release versions ("v3.8.0" or "3.8.0").
+package version
+
+import (
+	"strconv"
+	"strings"
+)
+
+// Compare returns -1, 0 or 1 as a is older than, equal to or newer than b, and
+// false when either side is not a plain MAJOR.MINOR.PATCH version.
+func Compare(a, b string) (int, bool) {
+	aParts, okA := parse(a)
+	bParts, okB := parse(b)
+	if !okA || !okB {
+		return 0, false
+	}
+	for i := range len(aParts) {
+		if aParts[i] > bParts[i] {
+			return 1, true
+		}
+		if aParts[i] < bParts[i] {
+			return -1, true
+		}
+	}
+	return 0, true
+}
+
+// Normalize strips surrounding space and a leading "v" from a version tag.
+func Normalize(v string) string {
+	return strings.TrimPrefix(strings.TrimSpace(v), "v")
+}
+
+func parse(v string) ([3]int, bool) {
+	var result [3]int
+	parts := strings.Split(Normalize(v), ".")
+	if len(parts) != 3 {
+		return result, false
+	}
+	for i, part := range parts {
+		n, err := strconv.Atoi(part)
+		if err != nil {
+			return result, false
+		}
+		result[i] = n
+	}
+	return result, true
+}

internal/util/version/version_test.go

@@ -0,0 +1,12 @@
+package version
+
+import "testing"
+
+func TestCompareRejectsUnexpectedFormats(t *testing.T) {
+	if _, ok := Compare("latest", "2.9.3"); ok {
+		t.Fatal("expected non-semver latest tag to be rejected")
+	}
+	if _, ok := Compare("v2.9", "2.9.3"); ok {
+		t.Fatal("expected short version to be rejected")
+	}
+}