fix: use spec-compliant `no-referrer` meta value (#8725)

`never` was removed from the Referrer Policy spec in 2016 and is
only honoured by current browsers as a legacy alias. Replace with
the spec-compliant `no-referrer` token.

Tested:
- Safari 26 (WebKit): Referer suppressed
- LibreWolf 150 (Gecko): Referer suppressed
- Chromium 149 (Blink): Referer suppressed
- SeaMonkey 2.53.23: ignores meta referrer regardless of value
  (pre-existing, unaffected by this change)

Closes https://github.com/FreshRSS/FreshRSS/issues/8718

Co-authored-by: Bjørn A. Andersen <polybjorn@users.noreply.github.com>

app/layout/layout.phtml

@@ -45,7 +45,7 @@
 		<meta name="msapplication-TileColor" content="#FFF" />
 		<meta name="theme-color" content="#FFF" />
 <?php if (!FreshRSS_Context::systemConf()->allow_referrer) { ?>
-		<meta name="referrer" content="never" />
+		<meta name="referrer" content="no-referrer" />
 <?php } ?>
 		<?= FreshRSS_View::headTitle() ?>
 <?php

app/layout/simple.phtml

@@ -33,7 +33,7 @@
 		<meta name="msapplication-TileColor" content="#FFF" />
 		<meta name="theme-color" content="#FFF" />
 <?php if (!FreshRSS_Context::systemConf()->allow_referrer) { ?>
-		<meta name="referrer" content="never" />
+		<meta name="referrer" content="no-referrer" />
 <?php } ?>
 		<?= FreshRSS_View::headTitle() ?>
 		<?php if ($this->rss_url != ''): ?>