Add unit tests, smoke test script, fix CI to debian-host + test job

- tests/test_catalog.py: 5 unit tests for PypiCatalog (fetch, cache, sort prefix, completions)
- tests/test_proxy.py: 5 unit tests for BicepProxy (framing, injection, list result, passthrough)
- tests/conftest.py: pytest asyncio_mode=auto config
- scripts/smoke_test.sh: end-to-end TCP + health smoke test script
- .gitea/workflows/ci.yml: split into test + build-and-deploy jobs (test blocks deploy)
  - runs-on: debian-host (was ubuntu-latest = broken)
  - test job installs deps + runs pytest before building image
- pyproject.toml: [project.optional-dependencies] dev = pytest + pytest-asyncio

tests/conftest.py

@@ -0,0 +1,5 @@
+import pytest
+
+# Enable asyncio mode for all tests
+def pytest_configure(config):
+    config.addinivalue_line("markers", "asyncio: mark test as async")