fix: use window.top.document for toast and max z-index

Gradio js= callbacks may run in a context where document.body is not
the visible page body. Use window.top.document to guarantee the toast
lands on the real page, and set z-index to INT_MAX so it clears all
Gradio overlays.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -2130,14 +2130,18 @@ _GLOBAL_JS = """
 
   // Toast notification — styled like ZeroGPU quota warnings.
   function _showRegenToast(message, isError) {
-    var t = document.createElement('div');
+    // Use window.top.document so the toast always lands on the visible page,
+    // regardless of whether this JS runs inside a Gradio shadow context.
+    var doc = (window.top && window.top.document) ? window.top.document : document;
+    var t = doc.createElement('div');
     t.style.cssText = 'position:fixed;bottom:24px;left:50%;transform:translateX(-50%);' +
-      'z-index:999999;padding:12px 20px;border-radius:8px;font-family:sans-serif;' +
-      'font-size:13px;max-width:480px;text-align:center;box-shadow:0 4px 20px rgba(0,0,0,.5);' +
+      'z-index:2147483647;padding:12px 20px;border-radius:8px;font-family:sans-serif;' +
+      'font-size:13px;max-width:520px;text-align:center;box-shadow:0 4px 20px rgba(0,0,0,.6);' +
       'background:' + (isError ? '#7a1c1c' : '#1c4a1c') + ';color:#fff;' +
-      'border:1px solid ' + (isError ? '#c0392b' : '#27ae60') + ';';
+      'border:1px solid ' + (isError ? '#c0392b' : '#27ae60') + ';' +
+      'pointer-events:none;';
     t.textContent = message;
-    document.body.appendChild(t);
+    doc.body.appendChild(t);
     setTimeout(function() {
       t.style.transition = 'opacity 0.5s';
       t.style.opacity = '0';