Add tests

[Erisa]

We need to test basic functionality, such as

• We can upload pastes from the tailnet URL
• We can retrieve the same paste from the tailnet URL
• We can also retrieve the paste from the funnel and HTTP_PORT URLs
• We cannot view the homepage with auth from funnel and HTTP_PORT URLs
• We cannot upload pastes from funnel and HTTP_PORT URLs
• The tclip CLI should work as intended (upload a paste, then you can retrieve that paste and it has the right content)