feat: add email-api service and email-api-models contract project

New internal service that centralises SMTP email sending.
- email-api-models: SendEmailRequest DTO, IEmailApiClient Refit interface, EmailApiSettings
- email-api: SmtpEmailDispatcher (MailKit), EmailController (POST /api/email/send),
  branded HTML shell wrapper, shared-Files-volume attachment support
- Protected by X-Internal-Api-Key via UseInternalApiKeyProtection()
- No exposed Docker port — internal network only (http://email-api:8080)

Closes #22

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/email-api/Program.cs

@@ -0,0 +1,54 @@
+using System.Reflection;
+using EmailApi.Services;
+using Models.Settings;
+using Serilog;
+using StartupHelpers;
+
+StartupExtensions.LoadDotEnvFile();
+
+const string ServiceName = "email-api";
+var appVersion = StartupExtensions.GetApplicationVersion(Assembly.GetExecutingAssembly());
+
+try
+{
+    var builder = WebApplication.CreateBuilder(args);
+
+    builder.ConfigureJsonSerilog(ServiceName, appVersion);
+    Log.Information("Starting {Service} version {AppVersion}", ServiceName, appVersion);
+
+    builder.AddAzureKeyVaultIfConfigured();
+
+    builder.Services.AddControllers();
+    builder.Services.AddSwaggerWithXmlComments(Assembly.GetExecutingAssembly(), "Email API");
+
+    builder.Services.Configure<SmtpSettings>(builder.Configuration.GetSection("Smtp"));
+    builder.Services.Configure<FileStorageSettings>(builder.Configuration.GetSection("FileStorage"));
+
+    builder.Services.AddScoped<SmtpEmailDispatcher>();
+
+    var app = builder.Build();
+
+    app.LogStartupDiagnostics(ServiceName);
+
+    app.UseDefaultSerilogRequestLogging();
+    app.UseJsonExceptionHandler(ServiceName);
+    app.UseSwaggerInDevelopment("Email API", "EmailAPI");
+
+    app.UseInternalApiKeyProtection();
+
+    app.UseRouting();
+    app.UseAuthorization();
+    app.MapControllers();
+
+    Log.Information("{Service} startup complete. Listening for requests...", ServiceName);
+    app.Run();
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "{Service} terminated unexpectedly", ServiceName);
+}
+finally
+{
+    Log.Information("Shutting down {Service}", ServiceName);
+    Log.CloseAndFlush();
+}