Add AI chat feature

server/modules/chat/service.ts

@@ -0,0 +1,13 @@
+import { convertToModelMessages, streamText } from "ai";
+import type { ChatModel } from "./model";
+import { openai } from "@ai-sdk/openai";
+
+export abstract class Chat {
+  static async streamText(chat: ChatModel["chat"]) {
+    return streamText({
+      model: openai("gpt-5.5"),
+      system: "You are Yae Miko from Genshin Impact",
+      messages: await convertToModelMessages(chat.messages),
+    });
+  }
+}