refactor: Convert monolithic app to modular architecture

This commit refactors the entire codebase from a monolithic structure to a
modular one. Key changes include:

-   Extracting core components (e.g., user authentication, data processing,
    API handlers) into their own distinct modules.
-   Implementing a new directory structure to support a modular design.
-   Updating all internal references and import paths to reflect the new
    architecture.

The new structure improves maintainability, scalability, and allows for
easier independent development of each module in the future.

controllers/contactController.js

@@ -0,0 +1,57 @@
+module.exports = (pool, transporter) => {
+    
+    // The main function that handles the form submission
+    const submitForm = async (req, res) => {
+        const { firstName, lastName, organization, email, phone, contactMethod, message } = req.body;
+
+        try {
+            // 1. Save submission to the database
+            const result = await pool.query(
+                `INSERT INTO submissions(first_name, last_name, organization, email, phone, contact_method, message) 
+                 VALUES($1, $2, $3, $4, $5, $6, $7) RETURNING *`,
+                [firstName, lastName, organization, email, phone, contactMethod, message]
+            );
+
+            console.log('Successfully saved submission to the database:', result.rows[0]);
+
+            // 2. Send the email notification
+            const mailOptions = {
+                from: `"Contact Form" <contact@dlseitz.dev>`,
+                to: process.env.EMAIL_RCPT,
+                subject: 'New Contact Form Submission',
+                html: `
+                    <h3>New Submission</h3>
+                    <ul>
+                        <li><strong>First Name:</strong> ${firstName}</li>
+                        <li><strong>Last Name:</strong> ${lastName}</li>
+                        <li><strong>Organization:</strong> ${organization}</li>
+                        <li><strong>Email:</strong> ${email}</li>
+                        <li><strong>Phone:</strong> ${phone}</li>
+                        <li><strong>Contact Method:</strong> ${contactMethod}</li>
+                    </ul>
+                    <p><strong>Message:</strong></p>
+                    <p>${message}</p>
+                `,
+            };
+
+            const emailInfo = await transporter.sendMail(mailOptions);
+            console.log('Message sent: %s', emailInfo.messageId);
+
+            res.status(200).json({
+                message: 'Form submitted successfully and saved to the database!',
+                dataReceived: req.body
+            });
+
+        } catch (err) {
+            console.error('An error occurred during form submission:', err.stack);
+            res.status(500).json({
+                message: 'An error occurred. Please try again.',
+                error: err.message
+            });
+        }
+    };
+
+    return {
+        submitForm,
+    };
+};