fix(editor): ignore Esc while a blocking operation owns the screen

The discard-confirm opened underneath the busy overlay, which sits at z-index 200 - blurred and half-clickable. Worse than the display: it let the user arbitrate closing the editor while a sync or a rotation was writing to the same entry.

js/app.js

@@ -5971,6 +5971,13 @@ function updateBusy(text) {
 function hideBusy() {
     const o = $('#busyOverlay'); if (o) o.classList.add('is-hidden');
 }
+// True while a blocking operation owns the screen. Anything that would open a
+// dialog has to check this: the overlay is above every modal, so a dialog
+// raised now is invisible under it.
+function isBusy() {
+    const o = $('#busyOverlay');
+    return !!o && !o.classList.contains('is-hidden');
+}
 
 function closeConfirm(value) {
     $('#confirmModal').classList.add('is-hidden');
@@ -7378,6 +7385,11 @@ async function init() {
         if (e.key !== 'Escape') return;
         if (!$('#slideover').classList.contains('is-open')) return;
         if (document.querySelector('.modal:not(.is-hidden)')) return;
+        // A long operation is running (sync, export, rotation…). The busy
+        // overlay sits above everything at z-index 200, so a discard-confirm
+        // opened now would render blurred underneath it — and answering it
+        // would race whatever the operation is doing to the same entry.
+        if (isBusy()) return;
         // Command palette is .cmd-palette, not .modal — it sits on top of
         // the editor, so its Esc must close IT (bubble handler), not pop
         // the editor's discard-confirm underneath.