feat(api-key): 增加 API Key 上次使用时间并补齐测试

backend/internal/handler/dto/api_key_mapper_last_used_test.go

@@ -0,0 +1,40 @@
+package dto
+
+import (
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAPIKeyFromService_MapsLastUsedAt(t *testing.T) {
+	lastUsed := time.Now().UTC().Truncate(time.Second)
+	src := &service.APIKey{
+		ID:         1,
+		UserID:     2,
+		Key:        "sk-map-last-used",
+		Name:       "Mapper",
+		Status:     service.StatusActive,
+		LastUsedAt: &lastUsed,
+	}
+
+	out := APIKeyFromService(src)
+	require.NotNil(t, out)
+	require.NotNil(t, out.LastUsedAt)
+	require.WithinDuration(t, lastUsed, *out.LastUsedAt, time.Second)
+}
+
+func TestAPIKeyFromService_MapsNilLastUsedAt(t *testing.T) {
+	src := &service.APIKey{
+		ID:     1,
+		UserID: 2,
+		Key:    "sk-map-last-used-nil",
+		Name:   "MapperNil",
+		Status: service.StatusActive,
+	}
+
+	out := APIKeyFromService(src)
+	require.NotNil(t, out)
+	require.Nil(t, out.LastUsedAt)
+}

backend/internal/handler/dto/mappers.go

@@ -77,6 +77,7 @@ func APIKeyFromService(k *service.APIKey) *APIKey {
 		Status:      k.Status,
 		IPWhitelist: k.IPWhitelist,
 		IPBlacklist: k.IPBlacklist,
+		LastUsedAt:  k.LastUsedAt,
 		Quota:       k.Quota,
 		QuotaUsed:   k.QuotaUsed,
 		ExpiresAt:   k.ExpiresAt,

backend/internal/handler/dto/types.go

@@ -38,6 +38,7 @@ type APIKey struct {
 	Status      string     `json:"status"`
 	IPWhitelist []string   `json:"ip_whitelist"`
 	IPBlacklist []string   `json:"ip_blacklist"`
+	LastUsedAt  *time.Time `json:"last_used_at"`
 	Quota       float64    `json:"quota"`      // Quota limit in USD (0 = unlimited)
 	QuotaUsed   float64    `json:"quota_used"` // Used quota amount in USD
 	ExpiresAt   *time.Time `json:"expires_at"` // Expiration time (nil = never expires)