fix(仪表盘): 修复缓存稳定性并补充测试

backend/internal/repository/dashboard_cache_test.go

@@ -0,0 +1,28 @@
+package repository
+
+import (
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewDashboardCacheKeyPrefix(t *testing.T) {
+	cache := NewDashboardCache(nil, &config.Config{
+		Dashboard: config.DashboardCacheConfig{
+			KeyPrefix: "prod",
+		},
+	})
+	impl, ok := cache.(*dashboardCache)
+	require.True(t, ok)
+	require.Equal(t, "prod:", impl.keyPrefix)
+
+	cache = NewDashboardCache(nil, &config.Config{
+		Dashboard: config.DashboardCacheConfig{
+			KeyPrefix: "staging:",
+		},
+	})
+	impl, ok = cache.(*dashboardCache)
+	require.True(t, ok)
+	require.Equal(t, "staging:", impl.keyPrefix)
+}