refactor starlette as API, langgraph from openrouter

chatgraph.py

@@ -0,0 +1,29 @@
+from typing import TypedDict
+from langgraph.graph import StateGraph, START
+from langgraph.checkpoint.memory import MemorySaver
+from langchain_openai import ChatOpenAI
+from os import getenv
+from dotenv import load_dotenv
+
+load_dotenv()
+
+class State(TypedDict):
+    messages: list
+
+llm = ChatOpenAI(
+  openai_api_key=getenv("OPENROUTER_API_KEY"),
+  openai_api_base=getenv("OPENROUTER_BASE_URL"),
+  model_name="qwen/qwen3-235b-a22b-07-25",
+)
+
+def call_model(state: State):
+    # simple memory trim example: keep last 20 messages
+    trimmed = state["messages"][-20:]
+    response = llm.invoke(trimmed)
+    return {"messages": [response]}
+
+workflow = StateGraph(State)
+workflow.add_node("model", call_model)
+workflow.add_edge(START, "model")
+memory = MemorySaver()
+app_graph = workflow.compile(checkpointer=memory)