fix: override meta block in calendar templates

Calendar templates extend post/index.html which includes _meta.html
expecting a `post` variable. In standalone events mode there's no
post — override with empty meta block.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/_types/calendar/index.html

@@ -1,5 +1,7 @@
 {% extends '_types/post/index.html' %}
 
+{% block meta %}{% endblock %}
+
 {% block post_header_child %}
   {% from '_types/root/_n/macros.html' import index_row with context %}
   {% call index_row('calendar-header-child', '_types/calendar/header/_header.html') %}

templates/_types/calendars/index.html

@@ -1,6 +1,6 @@
 {% extends '_types/post/admin/index.html' %}
 
-
+{% block meta %}{% endblock %}
 
 {% block post_admin_header_child %}
   {% from '_types/root/_n/macros.html' import index_row with context %}