fix(editor): guard the second Esc path against the busy overlay too

There are two Escape handlers: a capture-phase one for the editor and the global one-surface-per-keystroke chain. Only the first was guarded, so export - which reaches the editor through the global chain - still popped the discard-confirm under the overlay.

js/app.js

@@ -8139,6 +8139,12 @@ async function init() {
             e.preventDefault();
             openCheatsheet();
         } else if (e.key === 'Escape') {
+            // A blocking operation owns the screen (export, sync, rotation):
+            // the busy overlay is above every surface listed below, so nothing
+            // here is actually reachable — and the editor's discard-confirm
+            // would open invisible underneath it. Second Esc path; the
+            // capture-phase one for the editor carries the same guard.
+            if (isBusy()) return;
             // Close in priority order: confirm first (most modal-y), then the
             // palette — it OPENS OVER the info modals (Ctrl+K on top of the
             // cheatsheet), so it must close before them. ONE surface per