refactor(js): avoid use of window.XXX and move to import/export

- change worker: do not cache html pages (not necessary)
- remove use of window.XXX and maximize import/export,
  this will provide more clarety,
  show circular dependencies + you will benefit IDE help

static/js/core/icons.js

@@ -483,9 +483,8 @@ function replaceIconsInElement(container) {
 }
 
 // ── Expose globally ────────────────────────────────────────────
-window.oxiIcon = oxiIcon;
-window.replaceIconsInElement = replaceIconsInElement;
-window.OxiIcons = _ICONS;
+export { oxiIcon, replaceIconsInElement };
+export const OxiIcons = _ICONS;
 
 // ── Auto-replace: MutationObserver bridge ──────────────────────
 // Watches the DOM for new <i class="fa-..."> elements and converts them