Added pagination support to:
- ListCompanies: filter by role, search
- ListProducts: filter by seller, search
- ListOrders: filter by buyer, seller, status
- ListInventory: filter by expiring date, seller
New domain types:
- ProductFilter, ProductPage
- CompanyFilter, CompanyPage
- OrderFilter, OrderPage
- InventoryPage
All endpoints now return paginated responses with:
- items array
- total count
- current page
- page size
Updated MockRepository in both test files to match new signatures
