feat(api): parse endpoints pass EventBus into store writes

- api.parse_837 / parse_835: pass request.app.state.event_bus into store.add()
- conftest: autouse fixture wires a fresh EventBus onto app.state for every
  test, since TestClient does not invoke the FastAPI lifespan handler
  unless used as a context manager
- test_pubsub: split get_event_bus coverage into a raises-when-missing test
  and a returns-attached-bus test, both save/restore app.state.event_bus
  around the assertion so the autouse fixture's bus is preserved

Phase 2 complete: db init moved to lifespan, EventBus is the process-wide
publish point, and the two ingest endpoints publish claim_written /
remittance_written / activity_recorded events on every store.add().

backend/tests/conftest.py

@@ -19,10 +19,22 @@ import pytest
 
 @pytest.fixture(autouse=True)
 def _auto_init_db(tmp_path, monkeypatch):
-    """Point CYCLONE_DB_URL at a per-test SQLite file and init the schema."""
+    """Point CYCLONE_DB_URL at a per-test SQLite file and init the schema.
+
+    Also wires a fresh ``EventBus`` onto ``app.state`` because ``TestClient``
+    does not invoke the FastAPI lifespan handler unless used as a context
+    manager. The bus is reset between tests so subscribers don't leak.
+    """
     monkeypatch.setenv("CYCLONE_DB_URL", f"sqlite:///{tmp_path}/test.db")
     from cyclone import db
+    from cyclone.api import app
+    from cyclone.pubsub import EventBus
+
     db._reset_for_tests()
     db.init_db()
-    yield
-    db._reset_for_tests()
+    app.state.event_bus = EventBus()
+    try:
+        yield
+    finally:
+        app.state.event_bus = None
+        db._reset_for_tests()