fix: correct import path in failover_loop.go and failover_loop_test.go

Use github.com/Wei-Shaw/sub2api/internal/service instead of
sub2api/internal/service to match the module path in go.mod.

backend/internal/handler/failover_loop.go

@@ -5,7 +5,7 @@ import (
 	"log"
 	"time"
 
-	"sub2api/internal/service"
+	"github.com/Wei-Shaw/sub2api/internal/service"
 )
 
 // TempUnscheduler 用于 HandleFailoverError 中同账号重试耗尽后的临时封禁。

backend/internal/handler/failover_loop_test.go

@@ -5,7 +5,7 @@ import (
 	"testing"
 	"time"
 
-	"sub2api/internal/service"
+	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/stretchr/testify/require"
 )