Add fixture-based unit tests for audit commands

[keepithandy]

Goal

Build confidence in dev-kit by testing audit behavior against small fake project fixtures.

Proposed work

• Add fixture folders under tests/fixtures/ for clean, missing-file, and mismatched-version projects.
• Test audit, version, and report using those fixtures.
• Keep fixtures tiny so they are easy to understand and maintain.
• Avoid relying on a real DungeonDex checkout for tests.

Acceptance checks

• python -m unittest discover -s tests passes from a fresh checkout.
• Tests do not require network access.
• Tests do not modify fixture files.
• Failure messages explain which fixture/check failed.