Fix SSE route dependency and align architecture docs

backend/app/services/embedding/__init__.py

@@ -1,6 +1,18 @@
-"""嵌入和分块服务"""
+"""Initialize the app.services.embedding package."""
+# Keep package boundaries explicit so backend imports stay predictable.
 
-from .text_chunker import RegulationChunker
-from .bge_m3_embedder import BGEM3Embedder
 
 __all__ = ["RegulationChunker", "BGEM3Embedder"]
+
+
+def __getattr__(name: str):
+    """Handle getattr for this module."""
+    if name == "RegulationChunker":
+        from .text_chunker import RegulationChunker
+
+        return RegulationChunker
+    if name == "BGEM3Embedder":
+        from .bge_m3_embedder import BGEM3Embedder
+
+        return BGEM3Embedder
+    raise AttributeError(name)