Fix: Use robust copy fallback in code blocks

Co-authored-by: gemini-3.7-flash <noreply@google.com>

src/markdown.js

@@ -1,4 +1,5 @@
 import mathjax3 from 'https://esm.sh/markdown-it-mathjax3';
+import { copyToClipboard } from './utils.js';
 
 export const md = window.md = window.markdownit({ html: false, linkify: true, typographer: true, breaks: true }).use(mathjax3);
 
@@ -10,11 +11,10 @@ export function enhanceCodeBlocks(root, doHL = true) {
       const len = code.textContent.length, countText = len >= 1e3 ? (len / 1e3).toFixed(1) + 'K' : len;
       const $btn = window.$('<button class="bg-slate-900 text-white rounded-lg py-1 px-2 text-xs opacity-85">Copy</button>').on('click', async e => {
         e.stopPropagation();
-        try {
-          await navigator.clipboard.writeText(code.innerText);
+        if (await copyToClipboard(code.innerText)) {
           $btn.text('Copied');
           setTimeout(() => $btn.text('Copy'), 1200);
-        } catch { }
+        }
       });
       const $container = window.$('<div class="code-actions absolute top-2 right-2 flex items-center gap-2"></div>');
       $container.append(window.$(`<span class="text-xs text-gray-500">${countText} chars</span>`), $btn);