Fix SSE route dependency and align architecture docs

backend/app/application/documents/__init__.py

@@ -0,0 +1,7 @@
+"""Initialize the app.application.documents package."""
+
+from .services import DocumentCommandService, DocumentProcessResult, DocumentQueryService
+# Keep package boundaries explicit so backend imports stay predictable.
+
+
+__all__ = ["DocumentCommandService", "DocumentProcessResult", "DocumentQueryService"]