Purchases by month:
GET /api/purchases/report_by_month.php?start_date=2025-01-01&end_date=2025-12-31

Average purchase price per product:
GET /api/purchases/report_avg_price_by_product.php?limit=5

Top purchased products:
GET /api/purchases/report_top_products.php?limit=3

 do you want me to integrate purchase reporting into the frontend dashboard (e.g., monthly spend chart + product cost trends), so you can view both sales and purchases side by side?