deepseek_adapter.py had never been importable: it referenced ProviderAdapter
and ProfileConfig, neither of which exists in src/, and profile.extra, which
RouterProfileConfig does not define. Rewritten against BaseProviderAdapter with
the three missing abstract methods and registered as "deepseek".
Adds tests/test_import_invariants.py, which walks every shipped module and
fails on broken internal references while skipping absent optional GUI extras.
It also asserts that test modules importing customtkinter call
pytest.importorskip, since a missing guard aborts collection of the whole
session and takes the release gate with it.
Adds a headless CI job that uninstalls customtkinter and runs the suite, so
that invariant is enforced rather than remembered.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
