Add theme presets, gradient backgrounds, and macOS-style window chrome

Replaces the old light/dark toggle with 10 fixed color themes (plus
Black & Grey and White) that drive a coordinated gradient palette across
the whole admin UI, a Google Fonts picker, and a native-page dark-mode
stylesheet that now covers modals and plugin/theme card grids. Fixes
several background/gradient seams where the sidebar, toolbar, and content
frame were each painting their own independent copy of the page gradient
instead of sharing one continuous plane.

Also adds a macOS-style traffic-light title bar to every page (close,
minimize, maximize) and a persistent bottom taskbar so a minimized page
can be restored from anywhere, plus a Plugins management page.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/src/pages/settings/settingsConfig.js

@@ -94,17 +94,17 @@ export const settingsCategories = [
     icon: 'dashicons-admin-appearance',
     fields: [
       {
-        key: 'dark_mode',
-        type: 'toggle',
-        label: 'Dark mode',
-        description: 'Use the dark interface theme across the admin.',
+        key: 'theme_preset',
+        type: 'theme-picker',
+        label: 'Theme',
+        description: 'Pick a color for the whole admin interface.',
+        default: 'indigo',
       },
       {
-        key: 'accent_color',
-        type: 'color',
-        label: 'Accent color',
-        description: 'Primary accent color used throughout the interface.',
-        default: '#4772fa',
+        key: 'font_family',
+        type: 'font-picker',
+        label: 'Font family',
+        description: 'Google Font used across the Aurora interface.',
       },
     ],
   },