refactor(tests): reorganize tests into unittest/ and e2e/ directories

- Move all unit tests from tests/ to tests/unittest/
- Add tests/e2e/ directory for end-to-end tests
- Update conftest.py for new test structure
- Add new tests for auth dependencies, policies, route injection
- Add new tests for run callbacks, create store, execution artifacts
- Remove obsolete tests for deleted persistence layer

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/tests/unittest/test_sse_format.py

@@ -0,0 +1,30 @@
+"""Tests for SSE frame formatting utilities."""
+
+import json
+
+
+def _format_sse(event: str, data, *, event_id: str | None = None) -> str:
+    from app.gateway.routers.langgraph.runs import format_sse
+
+    return format_sse(event, data, event_id=event_id)
+
+
+def test_sse_end_event_data_null():
+    """End event should have data: null."""
+    frame = _format_sse("end", None)
+    assert "data: null" in frame
+
+
+def test_sse_metadata_event():
+    """Metadata event should include run_id and attempt."""
+    frame = _format_sse("metadata", {"run_id": "abc", "attempt": 1}, event_id="123-0")
+    assert "event: metadata" in frame
+    assert "id: 123-0" in frame
+
+
+def test_sse_error_format():
+    """Error event should use message/name format."""
+    frame = _format_sse("error", {"message": "boom", "name": "ValueError"})
+    parsed = json.loads(frame.split("data: ")[1].split("\n")[0])
+    assert parsed["message"] == "boom"
+    assert parsed["name"] == "ValueError"