feat: implement basic chat UI component

- Create App component with message list and input field
- Use Static component for message history
- Support user input with ink-text-input
- Simple echo response for demonstration

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: koki-develop

src/App.tsx

@@ -0,0 +1,63 @@
+import { Box, Static, Text } from "ink";
+import TextInput from "ink-text-input";
+import type React from "react";
+import { useState } from "react";
+
+interface Message {
+  id: number;
+  text: string;
+  sender: "user" | "assistant";
+}
+
+export const App: React.FC = () => {
+  const [messages, setMessages] = useState<Message[]>([
+    {
+      id: 1,
+      text: "こんにちは！何かお手伝いできることはありますか？",
+      sender: "assistant",
+    },
+  ]);
+  const [input, setInput] = useState("");
+
+  const handleSubmit = () => {
+    if (input.trim() === "") return;
+
+    const newMessage: Message = {
+      id: messages.length + 1,
+      text: input,
+      sender: "user",
+    };
+
+    setMessages([...messages, newMessage]);
+    setInput("");
+
+    // シンプルな応答を追加
+    setTimeout(() => {
+      const response: Message = {
+        id: messages.length + 2,
+        text: `「${input}」についてお答えします。`,
+        sender: "assistant",
+      };
+      setMessages((prev) => [...prev, response]);
+    }, 500);
+  };
+
+  return (
+    <Box flexDirection="column">
+      <Static items={messages}>
+        {(message) => (
+          <Box key={message.id} marginBottom={1}>
+            <Text color={message.sender === "user" ? "cyan" : "green"}>
+              {message.sender === "user" ? "あなた" : "アシスタント"}:{" "}
+              {message.text}
+            </Text>
+          </Box>
+        )}
+      </Static>
+      <Box>
+        <Text color="yellow">入力: </Text>
+        <TextInput value={input} onChange={setInput} onSubmit={handleSubmit} />
+      </Box>
+    </Box>
+  );
+};