Design a warehouse inventory management system.

warehouses(id, name, location, capacity) products(id, sku UNIQUE, name, category, weight_kg DECIMAL) inventory(warehouse_id FK, product_id FK, quantity INT CHECK(quantity >= 0), reserved_qty INT DEFAULT 0, PRIMARY KEY(warehouse_id, product_id)) inventory_transactions(id BIGSERIAL, warehouse_id FK, product_id FK, quantity INT, txn_type VARCHAR, reference_id, created_at, created_by) EXCLUDE or CHECK