feat: add settings window for Zen UI

src/browser/base/content/ZenUIManager.mjs

@@ -265,6 +265,14 @@ var gZenUIManager = {
   get panelUIPosition() {
     return gZenVerticalTabsManager._hasSetSingleToolbar ? 'bottomleft topleft' : 'bottomright topright';
   },
+
+  openSettingsWindow() {
+    window.openDialog(
+      "chrome://browser/content/zen-components/windows/zen-settings.xhtml",
+      "",
+      "centerscreen,chrome,modal,titlebar",
+    );
+  }
 };
 
 var gZenVerticalTabsManager = {

src/browser/base/content/zen-assets.jar.inc.mn

@@ -81,3 +81,6 @@
         # JS Vendor
         content/browser/zen-vendor/tsparticles.confetti.bundle.min.js (content/zen-vendor/tsparticles.confetti.bundle.min.js)
         content/browser/zen-vendor/motion.min.mjs                      (content/zen-vendor/motion.min.mjs)
+
+        # Windows
+        content/browser/zen-components/windows/zen-settings.xhtml (zen-components/windows/zen-settings.xhtml)

src/browser/base/zen-components/windows/zen-settings.xhtml

@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<!DOCTYPE window>
+
+<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        xmlns:html="http://www.w3.org/1999/xhtml"
+        id="zenSettingsWindow"
+        style="min-width: 40em;">
+
+</window>