Add Settings button to the bulk sender window

The ribbon button only opened SettingsForm while the archive folder
was unconfigured - once saved once, there was no way back into
settings (domain, templates, sender account, signature path) short of
breaking the saved folder path. Added a "Настройки..." button to
PreviewForm that reopens SettingsForm and rescans with the reloaded
settings afterward.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

outlook-bulk-sender/BulkArchiveMailer.AddIn/UI/PreviewForm.cs

@@ -172,6 +172,34 @@ namespace BulkArchiveMailer.AddIn.UI
             RunScan();
         }
 
+        private void btnSettings_Click(object sender, EventArgs e)
+        {
+            using (var settingsForm = new SettingsForm(outlookApplication))
+            {
+                settingsForm.ShowDialog(this);
+            }
+
+            // Regardless of DialogResult (OK or Cancel), reload settings and
+            // rescan so a changed archive folder, domain, or templates are
+            // reflected immediately without a separate "Пересканировать"
+            // click. A closed-without-saving dialog just reloads the same
+            // settings again, which is harmless.
+            try
+            {
+                settings = AppSettings.Load();
+            }
+            catch (Exception ex)
+            {
+                MessageBox.Show(this, "Не удалось прочитать настройки: " + ex.ToString(), "BulkArchiveMailer", MessageBoxButtons.OK, MessageBoxIcon.Error);
+                return;
+            }
+
+            signatureHtml = ResolveSignatureHtml();
+            lblSignatureWarning.Visible = string.IsNullOrEmpty(signatureHtml);
+
+            RunScan();
+        }
+
         private void btnCheckAllReady_Click(object sender, EventArgs e)
         {
             foreach (var row in rows)