fix(card): make the icon fallback onerror handler compile

The handler assigned through an optional chain,
this.nextElementSibling?.style.display='inline-block'. An optional chain
is not a valid assignment target, so the whole attribute failed to compile
("SyntaxError: Invalid left-hand side in assignment") whenever an icon
image failed to load: the broken image stayed visible and the fallback
<i> icon never appeared. An explicit null check does the same and
compiles.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/templates/moduls/card.html.j2

@@ -9,7 +9,7 @@
             src="{{ asset_src(card.icon) }}"
             alt="{{ card.title }}"
             style="width:100px; height:auto;"
-            onerror="this.style.display='none'; this.nextElementSibling?.style.display='inline-block';">
+            onerror="this.style.display='none'; if (this.nextElementSibling) this.nextElementSibling.style.display='inline-block';">
           {% if card.icon.class %}
             <i class="{{ card.icon.class }}" style="display:none;"></i>
           {% endif %}