Generate a detailed expense breakdown by category for a given period. Use when the user asks for an expense report, spending summary, Ausgabenübersicht, cost analysis, or wants to understand where their money is going.

为指定时段生成按类别划分的详细支出明细。当用户要求提供支出报告、消费摘要、Ausgabenübersicht、成本分析或想了解资金去向时使用。