Build the pytest coverage suite

[FriggemannMichael]

Objective:
Create a focused pytest suite that supports the required 95 percent coverage target.

Acceptance criteria:

• Tests cover authentication success and failure cases.
• Tests cover permissions for customer, business, owner, and staff behavior.
• Tests cover documented status codes for core endpoints.
• Tests cover serializer validation for offers, orders, profiles, and reviews.
• Coverage command can run from the local virtual environment.
• Coverage target in pyproject.toml remains at 95 percent.

[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.