feat: implement MessageHistory structure

src/brain/messageHistory.ts

@@ -0,0 +1,26 @@
+export type MessageSender = "persona" | "user";
+
+export interface MessageHistoryEntry {
+  sender: MessageSender;
+  time: Date;
+  content: string;
+}
+
+function formatTime(time: Date): string {
+  const pad = (n: number) => n.toString().padStart(2, "0");
+  return `${time.getFullYear()}-${pad(time.getMonth() + 1)}-${pad(
+    time.getDate(),
+  )} ${pad(time.getHours())}:${pad(time.getMinutes())}:${pad(time.getSeconds())}`;
+}
+
+export function translateMessageHistory(
+  personaName: string,
+  entries: ReadonlyArray<MessageHistoryEntry>,
+): string {
+  return entries
+    .map((entry) => {
+      const label = entry.sender === "persona" ? personaName : "사용자";
+      return `${label}@${formatTime(entry.time)}: ${entry.content}`;
+    })
+    .join("\n");
+}