fix: remove incorrect CSS escaping on color values

The Twig |e('css') filter was escaping '#' (0x23) to '\23 ' in hex
color values (bg_color, fg_color, error_color), causing browsers to
not recognize them as valid CSS colors. These are admin-configured
environment variables, not user input, so CSS escaping is unnecessary.

templates/_style.html.twig

@@ -1,10 +1,10 @@
 <style id="preauth-style">
 * { margin: 0; padding: 0.25em; }
-html { background-color: {{ env.bg_color|e('css') }}; color: {{ env.fg_color|e('css') }}; display: table;
+html { background-color: {{ env.bg_color }}; color: {{ env.fg_color }}; display: table;
     font-family: sans-serif; font-size: 1.5em; height: 100%; padding: 0; width: 100%; }
 body { display: table-cell; vertical-align: middle; }
 h1 { font-size: 2.5em; font-weight: normal; text-align: center; }
-p { color: {{ env.error_color|e('css') }}; text-align: center; }
+p { color: {{ env.error_color }}; text-align: center; }
 form { align-items: baseline; display: flex; flex-wrap: wrap; justify-content: center; }
 form div { width: 45%; min-width: 300px; }
 div.right { text-align: right; margin-top: 1em; padding-bottom: 0 }