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);

px-icon.js

@@ -15,6 +15,14 @@ const DEFAULT_AP_SIZE = 8;
 const DEFAULT_MODE = 'average';
 const SUPERSAMPLE = 8; // per grid cell, for point-sample mode
 
+// CSS custom properties (--pxicon-ap-size, --pxicon-mode, ...) aren't
+// observable the way DOM mutations/resizes are: MutationObserver and
+// ResizeObserver don't fire when a cascaded custom property changes.
+// Instances listen for this document-level event so config changes (e.g.
+// a page-level theme/control update) can trigger a re-check without every
+// caller needing to touch each <px-icon>'s internals.
+const REFRESH_EVENT = 'pxicon:refresh';
+
 // key -> Promise<HTMLCanvasElement> (the small pre-upscale grid raster)
 const rasterCache = new Map();
 
@@ -131,12 +139,15 @@ class PxIcon extends HTMLElement {
     // e.g. a morph swapping in a different icon.
     this._observer ??= new MutationObserver(() => this._scheduleRender());
     this._observer.observe(this, { childList: true, subtree: true, attributes: true, characterData: true });
+    this._refreshHandler ??= () => this._scheduleRender();
+    document.addEventListener(REFRESH_EVENT, this._refreshHandler);
     this._scheduleRender();
   }
 
   disconnectedCallback() {
     this._observer?.disconnect();
     this._resizeObserver?.disconnect();
+    document.removeEventListener(REFRESH_EVENT, this._refreshHandler);
   }
 
   _upgrade() {
@@ -219,4 +230,12 @@ class PxIcon extends HTMLElement {
 
 customElements.define('px-icon', PxIcon);
 
-export { PxIcon, rasterCache };
+// Call after changing a --pxicon-* custom property (e.g. on :root, or any
+// ancestor of a group of icons) to make every connected <px-icon> re-check
+// its computed config and re-render if it actually changed. Cheap to call
+// broadly: each instance's own key check skips the work if nothing did.
+function refreshAll() {
+  document.dispatchEvent(new CustomEvent(REFRESH_EVENT));
+}
+
+export { PxIcon, rasterCache, refreshAll };