refactor(js): move icons-page.js to dev_tools module

icons-page.js is a dev tool for browsing available icons, so it
belongs in dev_tools alongside testing-*.js and code-quality-*.js.

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

app/templates/admin/icons.html

@@ -318,5 +318,5 @@
 
 {% block extra_scripts %}
 {# ✅ CRITICAL: Load JavaScript file #}
-<script src="{{ url_for('static', path='admin/js/icons-page.js') }}"></script>
+<script src="{{ url_for('dev_tools_static', path='admin/js/icons-page.js') }}"></script>
 {% endblock %}