Email step: append SMTP debug trace to notes (and thus the report)

When debug capture is requested, the trace is now also appended to the
step's notes textarea with a clear --- SMTP debug trace ... --- header
and timestamp. This means:

- The technician can edit/trim the trace before finishing the session.
- It flows naturally into the Markdown + HTML report via the existing
  notes-in-report rendering — no special-casing needed.
- Pre-existing notes are preserved (appended to, not overwritten).
- Status is preserved.
- The collapsible details block on the step card still shows the raw
  capture for quick reference.

includes/steps/115-email.php

@@ -150,13 +150,26 @@ return new class extends WPH_Step {
         // mangle the formatting.
         $session = WPH_Session::current();
         if ($session && $debug_requested) {
+            $trace = array_slice($trace, 0, 200); // cap to avoid bloating the option
             $data = $session->data();
             $data['email_debug'] = [
                 'captured_at' => time(),
                 'transport'   => $transport,
-                'trace'       => array_slice($trace, 0, 200), // cap to avoid bloating the option
+                'trace'       => $trace,
             ];
             update_option(WPH_OPT_SESSION, $data, false);
+
+            // Append the trace to the step's notes so the technician can edit
+            // it and so it lands in the downloadable report (notes are
+            // already serialised verbatim).
+            $current_state = $session->step_state($this->id());
+            $current_notes = (string) $current_state['notes'];
+            $stamp = date('Y-m-d H:i');
+            $block  = "\n\n--- SMTP debug trace (" . $stamp . ", transport: " . $transport . ", to: " . $to . ") ---\n";
+            $block .= $trace ? implode("\n", $trace) : '(no trace lines captured — transport does not emit SMTP traffic)';
+            $block .= "\n--- end trace ---";
+            // Keep whatever status the technician had previously chosen.
+            $session->update_step($this->id(), (string) $current_state['status'], trim($current_notes . $block));
         }
 
         $time = date('Y-m-d H:i');