fix: sliders in demo require reload to rerender

CSS custom property changes (--pxicon-ap-size, --pxicon-mode) aren't
observed by MutationObserver/ResizeObserver, so a live-mounted <px-icon>
never rechecked its config. Add a pxicon:refresh document event + exported
refreshAll() helper; demo calls it from its control handlers.

examples/index.html

@@ -170,7 +170,7 @@
 </div>
 
 <script type="module">
-import '../px-icon.js';
+import { refreshAll } from '../px-icon.js';
 
 const apSizeInput = document.getElementById('apSize');
 const apSizeVal = document.getElementById('apSizeVal');
@@ -181,6 +181,7 @@ function applyConfig() {
   apSizeVal.textContent = ap;
   document.documentElement.style.setProperty('--pxicon-ap-size', ap + 'px');
   document.documentElement.style.setProperty('--pxicon-mode', modeSelect.value);
+  refreshAll();
 }
 apSizeInput.addEventListener('input', applyConfig);
 modeSelect.addEventListener('change', applyConfig);