fix: add isDestroyed guard in setApplicationMenu and TODO for getWindow fallback

Add isDestroyed() check in the setApplicationMenu interceptor to skip
destroyed windows when hiding menu bars, matching the defensive pattern
used elsewhere in the codebase.

Add TODO comment on getWindow() popup fallback limitation to flag that
callers like getIsMaximized() may behave unexpectedly when a popup is
returned instead of the main window.

Co-Authored-By: Claude <claude@anthropic.com>

scripts/claude-native-stub.js

@@ -13,6 +13,8 @@ function getWindow() {
     const { BrowserWindow } = require('electron');
     const focused = BrowserWindow.getFocusedWindow();
     if (focused) return focused;
+    // TODO: Fallback may return a popup window; callers like
+    // getIsMaximized() may behave unexpectedly on popups.
     const win = BrowserWindow.getAllWindows().find(
       (w) => !w.isDestroyed()
     );

scripts/frame-fix-wrapper.js

@@ -139,6 +139,7 @@ Module.prototype.require = function(id) {
       if (process.platform === 'linux') {
         // Hide menu bar on all existing windows after menu is set
         for (const win of module.BrowserWindow.getAllWindows()) {
+          if (win.isDestroyed()) continue;
           win.setMenuBarVisibility(false);
         }
         console.log('[Frame Fix] Menu bar hidden on all windows');