test(conftest): register tests.pytest_collection_order as pytest plugin

tests/conftest.py

@@ -22,6 +22,8 @@ if project_root not in sys.path:
 from defer.sugar import install
 install()
 
+pytest_plugins = ["pytest_collection_order"]
+
 # Per the user spec (startup_speedup_20260606 spec.md:2.2 Layer 3,
 # and the message in workflow.md about warmup notifications): the
 # AppController's warmup mechanism loads heavy modules on the _io_pool