refactor(webui): separate core/css into base/components/screens

core/css held 13 flat stylesheets. Grouped by role, matching the JS sub-system
split:

  core/css/base/        foundation (3): tokens, style, themes
  core/css/components/  chrome + widgets (7): topbar, sidebar, modal, forms,
                        config, update-notifier, aurora-background
  core/css/screens/     full-page screens (3): login, loading-screen,
                        setup-wizard

Path-only move (git mv) + href rewrite in index.html. No @import anywhere and
the <link> line order is unchanged, so the cascade is preserved; all 13 paths
verified to resolve.

Signed-off-by: librelad <librelad@digitalangels.vip>

containers/libreportal/frontend/index.html

@@ -11,33 +11,33 @@
 
   <!-- Styles -->
   <!-- Base token layer (theme-agnostic): --font-mono, --page-* identity hues -->
-  <link rel="stylesheet" href="/core/css/tokens.css">
-  <link rel="stylesheet" href="/core/css/themes.css">
-  <link rel="stylesheet" href="/core/css/loading-screen.css">
-  <link rel="stylesheet" href="/core/css/setup-wizard.css">
-  <link rel="stylesheet" href="/core/css/style.css">
+  <link rel="stylesheet" href="/core/css/base/tokens.css">
+  <link rel="stylesheet" href="/core/css/base/themes.css">
+  <link rel="stylesheet" href="/core/css/screens/loading-screen.css">
+  <link rel="stylesheet" href="/core/css/screens/setup-wizard.css">
+  <link rel="stylesheet" href="/core/css/base/style.css">
   <link rel="stylesheet" href="/components/admin/config/css/ip-whitelist.css">
   <link rel="stylesheet" href="/components/apps/port-manager/css/port-manager.css">
   <link rel="stylesheet" href="/components/backup/core/css/backup.css">
   <link rel="stylesheet" href="/components/admin/ssh/css/ssh.css">
   <link rel="stylesheet" href="/components/admin/core/css/admin.css">
   <link rel="stylesheet" href="/components/apps/services/css/services.css">
-  <link rel="stylesheet" href="/core/css/modal.css">
+  <link rel="stylesheet" href="/core/css/components/modal.css">
   <link rel="stylesheet" href="/components/apps/tools/css/tools.css">
   <link rel="stylesheet" href="/components/apps/routing/css/routing.css">
-  <link rel="stylesheet" href="/core/css/login.css">
-  <link rel="stylesheet" href="/core/css/aurora-background.css">
-  <link rel="stylesheet" href="/core/css/topbar.css">
-  <link rel="stylesheet" href="/core/css/sidebar.css">
+  <link rel="stylesheet" href="/core/css/screens/login.css">
+  <link rel="stylesheet" href="/core/css/components/aurora-background.css">
+  <link rel="stylesheet" href="/core/css/components/topbar.css">
+  <link rel="stylesheet" href="/core/css/components/sidebar.css">
   <link rel="stylesheet" href="/components/apps/core/css/apps-layout.css">
   <link rel="stylesheet" href="/components/apps/core/css/apps.css">
-  <link rel="stylesheet" href="/core/css/forms.css">
-  <link rel="stylesheet" href="/core/css/config.css">
+  <link rel="stylesheet" href="/core/css/components/forms.css">
+  <link rel="stylesheet" href="/core/css/components/config.css">
   <link rel="stylesheet" href="/components/apps/core/css/service-buttons.css">
   <link rel="stylesheet" href="/components/dashboard/css/dashboard.css">
   <link rel="stylesheet" href="/components/tasks/css/tasks.css">
   <link rel="stylesheet" href="/components/updater/css/updater.css">
-  <link rel="stylesheet" href="/core/css/update-notifier.css">
+  <link rel="stylesheet" href="/core/css/components/update-notifier.css">
   <script>
     // Inline data-theme bootstrap — runs before any rendering so the right
     // palette tokens resolve on first paint. Synchronously injects a