fix: use page_header_flex macro for platform health page

Replace page_header with page_header_flex to properly support
the call block pattern with refresh button.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/admin/platform-health.html

@@ -1,23 +1,15 @@
 {# app/templates/admin/platform-health.html #}
 {% extends "admin/base.html" %}
 {% from 'shared/macros/alerts.html' import loading_state, error_state %}
-{% from 'shared/macros/headers.html' import page_header %}
+{% from 'shared/macros/headers.html' import page_header_flex, refresh_button %}
 
 {% block title %}Platform Health{% endblock %}
 
 {% block alpine_data %}adminPlatformHealth(){% endblock %}
 
 {% block content %}
-{% call page_header("Platform Health", subtitle="System metrics, capacity monitoring, and scaling recommendations") %}
-    <button
-        @click="refresh()"
-        :disabled="loading"
-        class="flex items-center px-4 py-2 text-sm font-medium text-white bg-purple-600 rounded-lg hover:bg-purple-700 transition-colors disabled:opacity-50"
-    >
-        <span x-show="loading" x-html="$icon('spinner', 'w-4 h-4 mr-2')"></span>
-        <span x-show="!loading" x-html="$icon('refresh', 'w-4 h-4 mr-2')"></span>
-        Refresh
-    </button>
+{% call page_header_flex(title='Platform Health', subtitle='System metrics, capacity monitoring, and scaling recommendations') %}
+    {{ refresh_button(variant='primary') }}
 {% endcall %}
 
 {{ loading_state('Loading platform health...') }}