Let a form send from its own address in 1.15.1

Umut asked where a contact form's mail is sent from: it was the recipient
address, `From` equal to `To`. That breaks as soon as the recipient is a
mailbox at another provider, because most hosts only deliver mail that
claims an address of their own domain, and the provider's SPF/DMARC then
treats it as forged.

Each form now has an optional `sender` setting, validated like the
recipient; empty keeps the old behaviour, so stored forms need no
migration. Delivery uses `sender ?: recipient`; the reply-to field is
untouched. The administration shows the field under the recipient with a
note on why it matters. The pilot launch config moves to port 8091 because
8087 was held by another session.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/Controller/FormController.php

@@ -90,8 +90,10 @@ final class FormController extends AbstractController
         foreach ($form['fields'] as $field) {
             $lines[] = $field['label'].': '.($values[$field['name']] ?? '');
         }
+        // Der Absender ist die eigene Adresse des Formulars, sonst der Empfaenger. Viele Hoster
+        // liefern nur aus, was von einer Adresse ihrer eigenen Domain kommt.
         $email = (new Email())
-            ->from($form['settings']['recipient'])
+            ->from(($form['settings']['sender'] ?? '') ?: $form['settings']['recipient'])
             ->to($form['settings']['recipient'])
             ->subject($form['settings']['subject'])
             ->text(implode("\n", $lines)."\n\n-- \nGesendet über ".rtrim($this->siteOrigin, '/'));