semantic update

backend/src/app.py

@@ -241,6 +241,10 @@ frontend_path = project_root / "frontend" / "build"
 if frontend_path.exists():
     app.mount("/_app", StaticFiles(directory=str(frontend_path / "_app")), name="static")
 
+    # [DEF:serve_spa:Function]
+    # @PURPOSE: Serves the SPA frontend for any path not matched by API routes.
+    # @PRE: frontend_path exists.
+    # @POST: Returns the requested file or index.html.
     @app.get("/{file_path:path}", include_in_schema=False)
     async def serve_spa(file_path: str):
         # Only serve SPA for non-API paths