Fix SSE route dependency and align architecture docs

backend/app/domain/documents/__init__.py

@@ -0,0 +1,17 @@
+"""Initialize the app.domain.documents package."""
+
+from .models import Chunk, Document, DocumentStatus, ParsedDocument
+from .ports import ChunkBuilder, DocumentBinaryStore, DocumentParser, DocumentRepository
+# Keep package boundaries explicit so backend imports stay predictable.
+
+
+__all__ = [
+    "Chunk",
+    "Document",
+    "DocumentStatus",
+    "ParsedDocument",
+    "ChunkBuilder",
+    "DocumentBinaryStore",
+    "DocumentParser",
+    "DocumentRepository",
+]