Inventory Management API for a Warehouse System

Problem Description

A warehouse management company needs an API to track inventory across multiple warehouse locations. The system manages tens of thousands of inventory items and warehouse staff use a web dashboard to check stock levels, receive new shipments, and transfer items between locations.

Build a Python/Flask REST API that supports:

• Listing inventory items with filtering by warehouse location, category, and stock level (e.g., items below reorder threshold)
• Getting the details of a single inventory item
• Receiving new stock (creating a new inventory record or updating quantity of an existing item)
• Transferring stock between warehouses (decrement from source, increment at destination)
• Bulk receiving: processing a shipment manifest with dozens of items in a single API call
• Getting inventory summary by warehouse (total items, total value, items below reorder threshold)

Inventory items have: id, sku, name, category, quantity, unit_cost, reorder_threshold, warehouse_id, last_updated.

Output Specification

Implement the API in an app/ directory with an entry point at app/__init__.py or app.py. Use SQLite or in-memory storage.

Produce a requirements.txt with dependencies.

Do not start the server — just produce the source files.