fix(admin): expose updateCharCounter for Q-modal oninput handler

Phase 2 review caught this: updateCharCounter was defined inside

questions.js IIFE but never exposed via window.X; admin.html:1672

calls it via oninput, would throw ReferenceError on every keypress.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/js/admin/sections/questions.js

@@ -525,6 +525,7 @@
   window.handleImageFileSelect = handleImageFileSelect;
   window.importCSVFile = importCSVFile;
   window.downloadCSVTemplate = downloadCSVTemplate;
+  window.updateCharCounter = updateCharCounter;
   window.AdminSections = window.AdminSections || {};
   window.AdminSections.questions = {
     init: async () => { if (inited) return; inited = true; await load(); },