test(rmi-backend,audit): add tests __init__.py for package discovery

Phase 1 of AUDIT-2026-Q3.md item P1.2.

tests/ was not a Python package, so downstream imports
(`from tests.unit.x import y`, testcontainers config loading,
pytest --import-mode=importlib) failed without PYTHONPATH=.
Creating __init__.py in tests/, tests/unit/, tests/integration/
makes the suite a proper package. pytest collection already worked
via rootdir discovery (886 tests collected either way), but
*importing* test modules will now work.

Also seeds tests/integration/conftest.py with a Phase-1 stub
fixture. Phase 3 (testcontainers) replaces it.

Full fix lands in P1.3 (setuptools.packages = ["app"] +
tools.setuptools.package-data in pyproject.toml) — without that,
`pip install -e .` does not expose the app package.

tests/integration/conftest.py

@@ -0,0 +1,14 @@
+"""Shared fixtures for integration tests.
+
+Phase 1 stub — Phase 3 (AUDIT-2026-Q3) adds testcontainers fixtures for
+postgres, redis, qdrant.
+"""
+import pytest
+
+
+@pytest.fixture(scope="session")
+def event_loop_policy():
+    """Default asyncio policy. Phase 3 will replace with testcontainers."""
+    import asyncio
+
+    return asyncio.DefaultEventLoopPolicy()