fix: 修复域能相关数据表缺失及首次查询报错

- AutoMigrate 添加 EnergyLog、PostEnergizeLog、DailyExpSummary 三张表
- GetDailyEnergizeExp 无记录时返回 nil, nil 而非 gorm.ErrRecordNotFound
- 调用方增加 summary nil 检查，防止空指针

cmd/server/main.go

@@ -27,7 +27,7 @@ func main() {
 	if err != nil {
 		log.Fatalf("连接数据库失败: %v", err)
 	}
-	if err := db.AutoMigrate(&model.User{}, &model.AuditSubmission{}, &model.SiteSetting{}, &model.Notification{}, &model.Post{}, &model.UserCheckIn{}, &model.UserTask{}); err != nil {
+	if err := db.AutoMigrate(&model.User{}, &model.AuditSubmission{}, &model.SiteSetting{}, &model.Notification{}, &model.Post{}, &model.UserCheckIn{}, &model.UserTask{}, &model.EnergyLog{}, &model.PostEnergizeLog{}, &model.DailyExpSummary{}); err != nil {
 		log.Fatalf("数据库迁移失败: %v", err)
 	}