fix(tests): clean up two pre-existing failures before config work

- decnet/agent/app.py /health: drop leftover 'push-test-2' canary
  planted during live VM push verification and never cleaned up;
  test_health_endpoint asserts the exact dict shape.
- tests/test_factory.py: switch the lazy-engine check from
  mysql+aiomysql (not in pyproject) to mysql+asyncmy (the driver the
  project actually ships). The test does not hit the wire so the
  dialect swap is safe.

Both were red on `pytest tests/` before any config/auto-spawn work
began; fixing them here so the upcoming commits land on a green
full-suite baseline.

decnet/agent/app.py

@@ -59,7 +59,7 @@ class MutateRequest(BaseModel):
 
 @app.get("/health")
 async def health() -> dict[str, str]:
-    return {"status": "ok", "marker": "push-test-2"}
+    return {"status": "ok"}
 
 
 @app.get("/status")