feat(BE-47,48,49,50): implement inventory adjustment system

- Extend DB schema with product_warehouses and stock_logs tables
- Implement stock adjustment API (increase/decrease operations)
- Add comprehensive validation for all adjustment operations
- Implement audit log system for each adjustment with history tracking
- Include transaction handling, DTOs, seeders, and proper error handling
- Add adjustment history API with pagination and filtering

TODO: Integration testing pending

internal/entities/product_warehouse.go

@@ -10,7 +10,7 @@ type ProductWarehouse struct {
 	Id          uint           `json:"id" gorm:"primaryKey;autoIncrement"`
 	ProductId   uint           `json:"product_id" gorm:"not null"`
 	WarehouseId uint           `json:"warehouse_id" gorm:"not null"`
-	Quantity    int            `json:"quantity" gorm:"default:0"`
+	Quantity    float64            `json:"quantity" gorm:"default:0"`
 	CreatedAt   time.Time      `json:"created_at" gorm:"autoCreateTime"`
 	UpdatedAt   time.Time      `json:"updated_at" gorm:"autoUpdateTime"`
 	CreatedBy   uint           `json:"created_by" gorm:"not null"`