fix(notification): enable web smtp test with saved password

Allow Web SMTP egress on TCP 587 and reuse the saved channel password only when connection settings match.

Ref: IT-1601

HrynCo.NotificationService.Web/Controllers/Admin/AdminChannelsController.cs

@@ -138,8 +138,21 @@ public class AdminChannelsController(IMediator mediator) : Controller
     [HttpPost("test-smtp")]
     public async Task<IActionResult> TestSmtp([FromBody] TestSmtpRequest request, CancellationToken ct)
     {
+        var password = request.Password;
+        if (string.IsNullOrEmpty(password) && request.ChannelId is Guid channelId)
+        {
+            var channelResult = await mediator.Send(new GetEmailChannelQuery(channelId), ct);
+            if (!channelResult.IsSuccess || channelResult.Result?.Settings is not SmtpChannelSettings saved)
+                return Ok(new { success = false, message = "SMTP channel not found." });
+
+            if (!MatchesSavedSmtpConnection(request, saved))
+                return Ok(new { success = false, message = "Enter the password to test changed SMTP connection settings." });
+
+            password = saved.Password;
+        }
+
         var result = await mediator.Send(new TestSmtpCommand(
-            request.Host, request.Port, request.Username, request.Password,
+            request.Host, request.Port, request.Username, password ?? string.Empty,
             request.UseSsl, request.FromEmail, request.FromName, request.ToEmail), ct);
 
         if (!result.IsSuccess)
@@ -148,6 +161,12 @@ public class AdminChannelsController(IMediator mediator) : Controller
         return Ok(new { success = true, message = $"Test email sent to {request.ToEmail}." });
     }
 
+    private static bool MatchesSavedSmtpConnection(TestSmtpRequest request, SmtpChannelSettings saved) =>
+        string.Equals(request.Host, saved.Host, StringComparison.OrdinalIgnoreCase)
+        && request.Port == saved.Port
+        && string.Equals(request.Username, saved.Username, StringComparison.Ordinal)
+        && request.UseSsl == saved.UseSsl;
+
     // POST /admin/channels/{id}/test
     [HttpPost("{id:guid}/test")]
     public async Task<IActionResult> Test(Guid id, [FromBody] TestChannelRequest request, CancellationToken ct)
@@ -180,6 +199,3 @@ public class AdminChannelsController(IMediator mediator) : Controller
 }
 
 public record TestChannelRequest(string ToEmail);
-public record TestSmtpRequest(
-    string Host, int Port, string Username, string Password,
-    bool UseSsl, string FromEmail, string FromName, string ToEmail);

HrynCo.NotificationService.Web/Controllers/Admin/TestSmtpRequest.cs

@@ -0,0 +1,6 @@
+namespace HrynCo.NotificationService.Web.Controllers.Admin;
+
+public record TestSmtpRequest(
+    string Host, int Port, string Username, string Password,
+    bool UseSsl, string FromEmail, string FromName, string ToEmail,
+    Guid? ChannelId = null);

HrynCo.NotificationService.Web/Views/AdminChannels/Edit.cshtml

@@ -138,7 +138,7 @@
                 <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
             </div>
             <div class="modal-body">
-                <p class="text-muted small">Tests the current form settings — no need to save first.</p>
+                <p class="text-muted small">Tests the current form settings — no need to save first. For an existing channel, a blank password uses the saved password only when the SMTP connection settings are unchanged.</p>
                 <label for="testToEmail" class="form-label fw-semibold">Recipient Email</label>
                 <input type="email" id="testToEmail" class="form-control" placeholder="you@example.com" />
                 <div id="testResult" class="mt-3" style="display:none"></div>
@@ -173,7 +173,9 @@
         }
 
         const form = document.getElementById('channelForm');
+        const channelId = form.querySelector('[name="Id"]').value;
         const payload = {
+            channelId: channelId === '00000000-0000-0000-0000-000000000000' ? null : channelId,
             host: form.querySelector('[name="Host"]').value,
             port: parseInt(form.querySelector('[name="Port"]').value, 10),
             username: form.querySelector('[name="Username"]').value,