feat(backend): Replace Node.js API with .NET 8

This commit completes the migration of the backend service from a Node.js/Express application to an ASP.NET Core 8 Minimal API.

- Re-implemented all API endpoints in C# for improved performance and type safety.
- Updated the Gitea Actions workflow to use the `setup-dotnet` action, `dotnet publish` for building, and now caches NuGet packages.
- Modified the deployment to create an `appsettings.Production.json` file from Gitea secrets instead of a `.env` file.
- Updated the PM2 ecosystem configuration to run the application using the `dotnet` interpreter.

backend/JoaoLoureiro.Portfolio.Infrastructure/HealthCheck/SmtpHealthCheck.cs

@@ -0,0 +1,31 @@
+
+using JoaoLoureiro.Portfolio.Infrastructure.Settings;
+using MailKit.Net.Smtp;
+using MailKit.Security;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Microsoft.Extensions.Options;
+
+namespace JoaoLoureiro.Portfolio.Infrastructure.HealthCheck;
+
+public class SmtpHealthCheck(IOptions<SmtpSettings> smtpSettings) : IHealthCheck
+{
+    private readonly SmtpSettings _smtpSettings = smtpSettings.Value;
+
+    public async Task<HealthCheckResult> CheckHealthAsync(
+        HealthCheckContext context,
+        CancellationToken cancellationToken = default)
+    {
+        using var client = new SmtpClient();
+        try
+        {
+            await client.ConnectAsync(_smtpSettings.Host, _smtpSettings.Port, SecureSocketOptions.StartTlsWhenAvailable, cancellationToken);
+            await client.AuthenticateAsync(_smtpSettings.User, _smtpSettings.Pass, cancellationToken);
+            await client.DisconnectAsync(true, cancellationToken);
+            return HealthCheckResult.Healthy("SMTP server is responding correctly.");
+        }
+        catch (Exception ex)
+        {
+            return HealthCheckResult.Unhealthy("Failed to connect or authenticate with SMTP server.", exception: ex);
+        }
+    }
+}

backend/JoaoLoureiro.Portfolio.Infrastructure/JoaoLoureiro.Portfolio.Infrastructure.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="AspNetCore.HealthChecks.System" Version="9.0.0" />
+    <PackageReference Include="MailKit" Version="4.13.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\JoaoLoureiro.Portfolio.Application\JoaoLoureiro.Portfolio.Core.csproj" />
+  </ItemGroup>
+
+</Project>

backend/JoaoLoureiro.Portfolio.Infrastructure/Services/SmtpEmailSender.cs

@@ -0,0 +1,44 @@
+using JoaoLoureiro.Portfolio.Core.Interfaces;
+using JoaoLoureiro.Portfolio.Core.Models;
+using JoaoLoureiro.Portfolio.Infrastructure.Settings;
+using MailKit.Net.Smtp;
+using MailKit.Security;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using MimeKit;
+
+namespace JoaoLoureiro.Portfolio.Infrastructure.Services;
+
+public class SmtpEmailSender(IOptions<SmtpSettings> smtpSettings, ILogger<SmtpEmailSender> logger) : IEmailSender
+{
+    private readonly SmtpSettings _smtpSettings = smtpSettings.Value;
+    private readonly ILogger<SmtpEmailSender> _logger = logger;
+
+    public async Task SendEmailAsync(EmailToSend email, CancellationToken cancellationToken = default)
+    {
+        var mimeMessage = new MimeMessage();
+        var fromAddress = _smtpSettings.FromEmail ?? _smtpSettings.User;
+
+        mimeMessage.From.Add(new MailboxAddress(email.SenderName, fromAddress));
+        mimeMessage.To.Add(MailboxAddress.Parse(_smtpSettings.ReceivingEmail));
+        mimeMessage.ReplyTo.Add(MailboxAddress.Parse(email.ReplyToEmail));
+        mimeMessage.Subject = $"New Portfolio Contact: {email.SenderName}";
+
+        var builder = new BodyBuilder
+        {
+            TextBody = $"Name: {email.SenderName}\nEmail: {email.ReplyToEmail}\nMessage: {email.MessageBody}",
+            HtmlBody = $@"<p><strong>Name:</strong> {email.SenderName}</p>
+                        <p><strong>Email:</strong> <a href=""mailto:{email.ReplyToEmail}"">{email.ReplyToEmail}</a></p>
+                        <p><strong>Message:</strong></p>
+                        <p>{email.MessageBody.Replace("\n", "<br>")}</p>"
+        };
+        mimeMessage.Body = builder.ToMessageBody();
+
+        using var client = new SmtpClient();
+
+        await client.ConnectAsync(_smtpSettings.Host, _smtpSettings.Port, SecureSocketOptions.StartTlsWhenAvailable, cancellationToken);
+        await client.AuthenticateAsync(_smtpSettings.User, _smtpSettings.Pass, cancellationToken);
+        await client.SendAsync(mimeMessage, cancellationToken);
+        _logger.LogInformation("Email sent successfully to {Recipient}", _smtpSettings.ReceivingEmail);
+    }
+}

backend/JoaoLoureiro.Portfolio.Infrastructure/Settings/SmtpSettings.cs

@@ -0,0 +1,11 @@
+namespace JoaoLoureiro.Portfolio.Infrastructure.Settings;
+
+public class SmtpSettings
+{
+    public required string Host { get; set; }
+    public int Port { get; set; }
+    public required string User { get; set; }
+    public required string Pass { get; set; }
+    public string? FromEmail { get; set; }
+    public required string ReceivingEmail { get; set; }
+}