fix: add missing space to mail footer signature delimiter

The signature delimiter on the first line of the mail footer templates was
missing the trailing space required by the signature block convention
(RFC 3676). Without "-- " (dash-dash-space) followed by a line break, mail
clients cannot recognize and collapse the signature.

Fixes #41364

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Thomas Müller <1005065+DeepDiver1975@users.noreply.github.com>

Author: DeepDiver1975

changelog/unreleased/41364

@@ -0,0 +1,8 @@
+Bugfix: Add missing space to mail footer signature delimiter
+
+We've fixed the signature delimiter in the email footer templates. The delimiter
+on the first line was missing the trailing space required by the signature block
+convention (RFC 3676), so mail clients were unable to recognize and collapse the
+signature. The delimiter is now correctly written as "-- " (dash-dash-space).
+
+https://github.com/owncloud/core/issues/41364

core/templates/html.mail.footer.php

@@ -1,4 +1,4 @@
---<br>
+-- <br>
 <?php p($theme->getName()); ?> -
 <?php p($theme->getSlogan()); ?>
 <br><a href="<?php p($theme->getBaseUrl()); ?>"><?php p($theme->getBaseUrl());?></a>

core/templates/plain.mail.footer.php

@@ -1,4 +1,4 @@
---
+-- 
 <?php p($theme->getName() . ' - ' . $theme->getSlogan()); ?>
 <?php
 p("\n" . $theme->getBaseUrl());