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/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,