```javascript
const express = require('express');
const path = require('path');
const app = express();
const PORT = 3000;

// Middleware
app.use(express.static(path.join(__dirname)));
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

// Stockage en mémoire (à remplacer par une base de données)
let users = [];
let appointments = [];

// Routes
app.get('/', (req, res) => {
    res.sendFile(path.join(__dirname, 'index.html'));
});

app.get('/register', (req, res) => {
    res.sendFile(path.join(__dirname, 'register.html'));
});

app.get('/login', (req, res) => {
    res.sendFile(path.join(__dirname, 'login.html'));
});

app.get('/dashboard', (req, res) => {
    res.sendFile(path.join(__dirname, 'dashboard.html'));
});

// API endpoints
app.post('/api/register', (req, res) => {
    const { name, email, password } = req.body;
    
    // Vérifier si l'utilisateur existe déjà
    const existingUser = users.find(u => u.email === email);
    if (existingUser) {
        return res.status(400).json({ error: 'Cet email est déjà utilisé' });
    }
    
    // Créer un nouvel utilisateur
    const newUser = { name, email, password };
    users.push(newUser);
    
    res.status(201).json({ message: 'Inscription réussie', user: newUser });
});

app.post('/api/login', (req, res) => {
    const { email, password } = req.body;
    
    // Vérifier les identifiants
    const user = users.find(u => u.email === email && u.password === password);
    if (!user) {
        return res.status(401).json({ error: 'Identifiants incorrects' });
    }
    
    res.json({ message: 'Connexion réussie', user });
});

app.post('/api/appointments', (req, res) => {
    const { userId, laboratory, date, time, analysis } = req.body;
    
    // Créer un nouveau rendez-vous
    const newAppointment = {
        id: Date.now(),
        userId,
        laboratory,
        date,
        time,
        analysis,
        status: 'confirmé'
    };
    
    appointments.push(newAppointment);
    
    res.status(201).json({ message: 'Rendez-vous pris avec succès', appointment: newAppointment });
});

app.get('/api/appointments/:userId', (req, res) => {
    const { userId } = req.params;
    const userAppointments = appointments.filter(a => a.userId === userId);
    
    res.json(userAppointments);
});

app.delete('/api/appointments/:id', (req, res) => {
    const { id } = req.params;
    const appointmentId = parseInt(id);
    
    appointments = appointments.filter(a => a.id !== appointmentId);
    
    res.json({ message: 'Rendez-vous annulé' });
});

// Démarrer le serveur
app.listen(PORT, () => {
    console.log(`Serveur démarré sur http://localhost:${PORT}`);
});
```