docs: -adding lesson 2

lessons/02-first-ai-app/characters/app.js

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+import express from 'express';
+import { OpenAI } from 'openai';
+import path from 'path';
+import { fileURLToPath } from 'url';
+import dotenv from 'dotenv';
+
+dotenv.config();
+
+const app = express();
+const port = process.env.PORT || 3000;
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+app.use(express.json());
+
+// Serve static files from the 'public' directory
+app.use(express.static(path.join(__dirname, 'public')));
+
+// Serve index.html on the default route
+app.get('/', (req, res) => {
+  res.sendFile(path.join(__dirname, 'public', 'index.html'));
+});
+
+// Route to send the prompt
+app.post('/send', async (req, res) => {
+  const { message } = req.body;
+  const prompt = message;
+
+  const messages = [
+    {
+      "role": "system",
+      "content": "You are Leonardo da Vinci, a brilliant inventor and artist. Limit your responses to only the time you live in, you don't know anything else. You only want to talk about your inventions and art, and possibly new ideas you have.",
+    },
+    {
+      "role": "user",
+      "content": prompt
+    }
+  ];
+
+  const openai = new OpenAI({
+    baseURL: "https://models.inference.ai.azure.com",
+    apiKey: process.env.GITHUB_TOKEN,
+  });
+
+  try {
+    console.log(`sending prompt ${prompt}`)
+    const completion = await openai.chat.completions.create({
+      model: 'gpt-4o-mini',
+      messages: messages,
+    });
+
+    res.json({
+      prompt: prompt,
+      answer: completion.choices[0]?.message?.content
+    });
+  } catch (error) {
+    res.status(500).json({ error: error.message });
+  }
+});
+
+app.listen(port, () => {
+  console.log(`Server is running on http://localhost:${port}`);
+});