feat: improve frontend accessibility, dark mode, and UX

- Replace div with semantic button elements in AppLayout for accessibility
- Use Ant Design theme tokens instead of hardcoded colors in MailDetailPage
- Add loading state to refresh buttons and pagination info
- Add German empty state messages to tables
- Clean up unnecessary ConfigProvider wrappers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

paperless-frontend/src/pages/PosteingangPage.tsx

@@ -1,7 +1,9 @@
 import { useEffect, useState } from 'react';
-import { Table, Popover, Button, Space, message, ConfigProvider, Tooltip } from 'antd';
+import { Table, Popover, Button, Space, message, Tooltip, Typography } from 'antd';
 import { AuthImage } from '../utils/auth-resource';
 import { ReloadOutlined } from '@ant-design/icons';
+
+const { Title } = Typography;
 import dayjs from 'dayjs';
 import { posteingangApi } from '../api/posteingang';
 import type { PosteingangDocument } from '../api/posteingang';
@@ -98,7 +100,7 @@ export default function PosteingangPage() {
       render: (text: string) => dayjs(text).format('DD.MM.YYYY HH:mm'),
     },
     {
-      title: 'Aktion',
+      title: 'Aktionen',
       key: 'action',
       width: 150,
       render: (_: any, record: PosteingangDocument) => (
@@ -110,10 +112,9 @@ export default function PosteingangPage() {
   ];
 
   return (
-    <ConfigProvider>
-      <div style={{ padding: '0 24px 24px' }}>
-        <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: 16 }}>
-            <h2>Posteingang</h2>
+    <div>
+      <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: 16 }}>
+            <Title level={3} style={{ margin: 0 }}>Posteingang</Title>
             <Space>
                 <Tooltip title="Manuell aktualisieren">
                     <Button icon={<ReloadOutlined />} onClick={fetchData} loading={loading} />
@@ -125,9 +126,10 @@ export default function PosteingangPage() {
           dataSource={data} 
           rowKey="id" 
           loading={loading}
-          pagination={{ pageSize: 20 }}
+          pagination={{ pageSize: 20, showSizeChanger: true, showTotal: (t) => `${t} Dokumente` }}
+          locale={{ emptyText: 'Keine Einträge vorhanden' }}
         />
-        
+
         <DocumentEditModal
             documentId={selectedDoc?.id || null}
             document={selectedDoc}
@@ -137,7 +139,6 @@ export default function PosteingangPage() {
             isPosteingang={true}
             hasNextDocument={data.length > 1}
         />
-      </div>
-    </ConfigProvider>
+    </div>
   );
 }