refactor: standardize admin templates with shared macros

Migrate all admin templates to use standardized components:
- Use tabs macros (tabs_nav, tab_button) for tab navigation
- Use number_stepper for quantity/numeric inputs
- Use headers macros for consistent page layouts
- Use modals macros for dialog components

Affected pages: dashboard, settings, logs, content-pages, companies,
vendors, users, imports, marketplace, code-quality, and more.

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

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

app/templates/admin/test-vendors-users-migration.html

@@ -1,21 +1,12 @@
 {# app/templates/admin/test-vendors-users-migration.html #}
 {% extends 'admin/base.html' %}
+{% from 'shared/macros/headers.html' import page_header %}
 
 {% block title %}Vendors & Users Migration Testing{% endblock %}
 
 {% block content %}
 <div x-data="migrationTest()" x-init="init()">
-    {# Page Header #}
-    <div class="flex flex-col md:flex-row md:items-center md:justify-between mb-8">
-        <div>
-            <h2 class="text-2xl font-semibold text-gray-700 dark:text-gray-200">
-                Vendors & Users Migration Testing
-            </h2>
-            <p class="text-gray-600 dark:text-gray-400 mt-1">
-                Comprehensive test suite for verifying the Jinja2 migration
-            </p>
-        </div>
-    </div>
+    {{ page_header('Vendors & Users Migration Testing', subtitle='Comprehensive test suite for verifying the Jinja2 migration') }}
 
     {# Status Cards #}
     <div class="grid gap-6 mb-8 md:grid-cols-2 xl:grid-cols-4">