3 张表
- clients：name, contact, hourly_rate, payment_terms
- projects：client, title, status, deliverables, due_date
- invoices：client, period, items[], amount, status, sent_at
月结 Agent 任务
On the last working day of each month:
- list projects delivered or partly delivered this month
- group by client
- draft invoices using Templates/invoice.md
- save to Invoices/<client>-<YYYY-MM>.md
- mark invoices table rows as "drafted, not sent"