test(notification): add email notification preview endpoints

Expose signed and received notification endpoints, with reset random payload variants, to exercise rendering and delivery without running a full envelope workflow.

Fall back to a fixed recipient when no email is supplied.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Controllers/NotificationController.cs

@@ -0,0 +1,88 @@
+using EnvelopeGenerator.Application.Common.Interfaces.Services.Notification;
+using EnvelopeGenerator.Domain.Constants;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace EnvelopeGenerator.Server.Controllers;
+
+/// <summary>
+/// Sends envelope notifications, optionally with randomly generated payloads.
+/// </summary>
+/// <remarks>
+/// Initializes a new instance of the <see cref="NotificationController"/> class.
+/// </remarks>
+[ApiController]
+[Route("api/[controller]")]
+public class NotificationController(IEnvelopeNotificationService notificationService) : ControllerBase
+{
+    private const string FallbackEmail = "htek0100@gmail.com";
+
+    /// <summary>
+    /// Sends the supplied document signed notification.
+    /// </summary>
+    [HttpPost("signed")]
+    public async Task<IActionResult> SendSigned(
+        [FromBody] DocumentSignedNotification notification,
+        [FromQuery] string? email,
+        CancellationToken cancel)
+    {
+        await notificationService.Notify(NormalizeEmail(email), notification, cancel);
+        return Ok();
+    }
+
+    /// <summary>
+    /// Sends a randomly generated document signed notification.
+    /// </summary>
+    [HttpPost("signed/random")]
+    public async Task<IActionResult> SendSignedRandom(
+        [FromQuery] string? email,
+        CancellationToken cancel)
+    {
+        await notificationService.Notify(NormalizeEmail(email), new DocumentSignedNotification
+        {
+            DocumentTitle = $"Dokument {Random.Shared.Next(1000, 9999)}",
+            NameReceiver = $"Empfänger {Random.Shared.Next(1, 100)}",
+            IsReadAndConfirm = Random.Shared.Next(2) == 0,
+        }, cancel);
+        return Ok();
+    }
+
+    /// <summary>
+    /// Sends the supplied document received notification.
+    /// </summary>
+    [HttpPost("received")]
+    public async Task<IActionResult> SendReceived(
+        [FromBody] DocumentReceivedNotification notification,
+        [FromQuery] string? email,
+        CancellationToken cancel)
+    {
+        await notificationService.Notify(NormalizeEmail(email), notification, cancel);
+        return Ok();
+    }
+
+    /// <summary>
+    /// Sends a randomly generated document received notification.
+    /// </summary>
+    [HttpPost("received/random")]
+    public async Task<IActionResult> SendReceivedRandom(
+        [FromQuery] string? email,
+        CancellationToken cancel)
+    {
+        await notificationService.Notify(NormalizeEmail(email), new DocumentReceivedNotification
+        {
+            DocumentTitle = $"Dokument {Random.Shared.Next(1000, 9999)}",
+            NameReceiver = $"Empfänger {Random.Shared.Next(1, 100)}",
+            NameSender = $"Absender {Random.Shared.Next(1, 100)}",
+            IsReadAndConfirm = Random.Shared.Next(2) == 0,
+            AdvancedSignature = Random.Shared.Next(2) == 0,
+            Origin = new Uri($"{Request.Scheme}://{Request.Host}"),
+            EnvelopeUuid = Guid.NewGuid().ToString(),
+            ReceiverSignature = Guid.NewGuid().ToString(),
+            Message = $"Testnachricht {Random.Shared.Next(1000, 9999)}"
+        }, cancel);
+        return Ok();
+    }
+
+    private static string NormalizeEmail(string? email)
+        => string.IsNullOrWhiteSpace(email) ? FallbackEmail : email;
+}