规范化xml内容，并在xml中添加仿真设置，规范化版本号等内容，补充xml规范md文件

app/main.py

@@ -14,6 +14,8 @@ from pydantic import BaseModel, Field
 app = FastAPI(title="System Simulation ReactFlow App")
 FRONTEND_DIST_DIR = Path(__file__).resolve().parent.parent / "frontend" / "dist"
 PROJECT_STORAGE_DIR = Path(__file__).parent / "data" / "reactflow-projects"
+SYSTEM_XML_SCHEMA_VERSION = "1"
+SYSTEM_XML_UNIT_SYSTEM = "SI"
 
 
 class ReactFlowPosition(BaseModel):
@@ -190,7 +192,25 @@ def simulate_reactflow_testmodel(payload: ReactFlowProjectPayload) -> dict[str,
 
 
 def build_reactflow_system_xml(project: ReactFlowProjectPayload) -> bytes:
-    system = ET.Element("System", {"name": project.name})
+    system = ET.Element(
+        "System",
+        {
+            "name": project.name,
+            "schemaVersion": SYSTEM_XML_SCHEMA_VERSION,
+            "unitSystem": SYSTEM_XML_UNIT_SYSTEM,
+        },
+    )
+    ET.SubElement(
+        system,
+        "Simulation",
+        {
+            "tStart": str(project.simulation.t_start),
+            "tStop": str(project.simulation.t_stop),
+            "step": str(project.simulation.step),
+            "maxStep": str(project.simulation.max_step),
+            "method": project.simulation.method,
+        },
+    )
     components_node = ET.SubElement(system, "Components")
     connections_node = ET.SubElement(system, "Connections")