feat: expose user activity timestamps in admin list

backend/internal/handler/dto/mappers.go

@@ -21,6 +21,8 @@ func UserFromServiceShallow(u *service.User) *User {
 		Concurrency:                u.Concurrency,
 		Status:                     u.Status,
 		AllowedGroups:              u.AllowedGroups,
+		LastLoginAt:                u.LastLoginAt,
+		LastActiveAt:               u.LastActiveAt,
 		CreatedAt:                  u.CreatedAt,
 		UpdatedAt:                  u.UpdatedAt,
 		BalanceNotifyEnabled:       u.BalanceNotifyEnabled,

backend/internal/handler/dto/types.go

@@ -7,16 +7,18 @@ import (
 )
 
 type User struct {
-	ID            int64     `json:"id"`
-	Email         string    `json:"email"`
-	Username      string    `json:"username"`
-	Role          string    `json:"role"`
-	Balance       float64   `json:"balance"`
-	Concurrency   int       `json:"concurrency"`
-	Status        string    `json:"status"`
-	AllowedGroups []int64   `json:"allowed_groups"`
-	CreatedAt     time.Time `json:"created_at"`
-	UpdatedAt     time.Time `json:"updated_at"`
+	ID            int64      `json:"id"`
+	Email         string     `json:"email"`
+	Username      string     `json:"username"`
+	Role          string     `json:"role"`
+	Balance       float64    `json:"balance"`
+	Concurrency   int        `json:"concurrency"`
+	Status        string     `json:"status"`
+	AllowedGroups []int64    `json:"allowed_groups"`
+	LastLoginAt   *time.Time `json:"last_login_at,omitempty"`
+	LastActiveAt  *time.Time `json:"last_active_at,omitempty"`
+	CreatedAt     time.Time  `json:"created_at"`
+	UpdatedAt     time.Time  `json:"updated_at"`
 
 	// 余额不足通知
 	BalanceNotifyEnabled       bool               `json:"balance_notify_enabled"`

backend/internal/handler/dto/user_mapper_activity_test.go

@@ -0,0 +1,32 @@
+package dto
+
+import (
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUserFromServiceAdmin_MapsActivityTimestamps(t *testing.T) {
+	t.Parallel()
+
+	lastLoginAt := time.Date(2026, time.April, 20, 10, 0, 0, 0, time.UTC)
+	lastActiveAt := lastLoginAt.Add(15 * time.Minute)
+
+	out := UserFromServiceAdmin(&service.User{
+		ID:           42,
+		Email:        "admin@example.com",
+		Username:     "admin",
+		Role:         service.RoleAdmin,
+		Status:       service.StatusActive,
+		LastLoginAt:  &lastLoginAt,
+		LastActiveAt: &lastActiveAt,
+	})
+
+	require.NotNil(t, out)
+	require.NotNil(t, out.LastLoginAt)
+	require.NotNil(t, out.LastActiveAt)
+	require.WithinDuration(t, lastLoginAt, *out.LastLoginAt, time.Second)
+	require.WithinDuration(t, lastActiveAt, *out.LastActiveAt, time.Second)
+}