19 tests covering ApiClient's full public surface: default and custom
origins, X-Client-Package and X-Auth-Token headers, getJSON with query
params, postJSON with JSON body, ApiError on 4xx/5xx, streaming file
and thumbnail downloads, and self-hosted origin routing.
Tests inject a recording fetch via the constructor, so nothing hits the
network. The test file is documented to serve as canonical usage
reference per the development workflow.
