Implement order workflow and order count endpoints

[FriggemannMichael]

Objective:
Implement the order API and business order counters.

Acceptance criteria:

• GET /api/orders/ returns orders related to the authenticated customer or business user.
• POST /api/orders/ creates an order from offer_detail_id and requires a customer user.
• PATCH /api/orders/{id}/ updates status and requires a business user with permission.
• DELETE /api/orders/{id}/ is restricted to staff users.
• GET /api/order-count/{business_user_id}/ returns order_count for in_progress orders.
• GET /api/completed-order-count/{business_user_id}/ returns completed_order_count for completed orders.
• Status values are limited to in_progress, completed, and cancelled.

[FriggemannMichael]

TDD workflow for this project:

• Define the expected behavior before implementing the endpoint or model behavior.
• Write or outline the failing test first.
• Implement only enough code to make that test pass.
• Refactor after the test passes.
• Keep Django check, Ruff, and the relevant tests green from the local virtual environment.