fix(logger): fix data race in InitLogger

Replace the package logger variable with an atomic.Pointer so InitLogger swapping the handle no longer races with concurrent Debug/Info/Warning/Error calls from other goroutines. Also guard fileRotate with a mutex, and add a regression test that reproduces the race under concurrent logging.

internal/logger/logger_test.go

@@ -2,7 +2,10 @@ package logger
 
 import (
 	"fmt"
+	"sync"
 	"testing"
+
+	golog "github.com/op/go-logging"
 )
 
 // TestGetLogs_ReturnsAtMostC guards the documented "up to c entries" contract.
@@ -28,3 +31,30 @@ func TestGetLogs_ReturnsAtMostC(t *testing.T) {
 		}
 	}
 }
+
+// InitLogger replaces the package logger while other goroutines are already
+// logging — CI caught that as a data race between InitLogger and Warningf.
+func TestInitLoggerConcurrentWithLogging(t *testing.T) {
+	t.Setenv("XUI_LOG_FOLDER", t.TempDir())
+
+	stop := make(chan struct{})
+	var logging sync.WaitGroup
+	logging.Add(1)
+	go func() {
+		defer logging.Done()
+		for {
+			select {
+			case <-stop:
+				return
+			default:
+				Warningf("concurrent %s", "log")
+			}
+		}
+	}()
+
+	for range 10 {
+		InitLogger(golog.CRITICAL)
+	}
+	close(stop)
+	logging.Wait()
+}