feat(web): 整体替换 UI 框架为 Ant Design 6 并接入自定义主题

以 antd ConfigProvider + antd-style 承载 zinc 风格自定义主题（明暗双套 token），
button/input/select/notification 用 createStyles 定制；三态主题经
darkAlgorithm 无刷新切换；use-toast 改基于 antd notification；
移除 shadcn/ui 组件目录与 radix 依赖；样式桥接层保证排版与多端布局不变。

web/src/pages/Note.tsx

@@ -1,6 +1,7 @@
-import { Link, useParams } from 'react-router'
+import { Link, useNavigate, useParams } from 'react-router'
 import { useQuery } from '@tanstack/react-query'
 import { ArrowLeft, ArrowRight, Clock, Eye } from 'lucide-react'
+import { Alert, Button, Card, Tag } from 'antd'
 import { api } from '../lib/api'
 import type { NoteDetail } from '../lib/api'
 import { useAuth } from '../lib/auth'
@@ -10,6 +11,7 @@ import { formatDateISO, readingMinutes } from '../lib/utils'
 
 export default function Note() {
   const { slug = '' } = useParams()
+  const navigate = useNavigate()
   const { authenticated } = useAuth()
   const { data: note, isLoading, error } = useQuery({
     queryKey: ['note', slug],
@@ -24,7 +26,9 @@ export default function Note() {
       <div className="pn-note-article">
         <p className="pn-home-list-empty">笔记不存在或未公开</p>
         <p style={{ textAlign: 'center', marginTop: -40 }}>
-          <Link to="/" className="btn ghost pn-note-back"><ArrowLeft size={14} />返回首页</Link>
+          <Button type="text" size="small" className="pn-note-back" icon={<ArrowLeft size={14} />} onClick={() => navigate('/')}>
+            返回首页
+          </Button>
         </p>
       </div>
     )
@@ -34,15 +38,23 @@ export default function Note() {
 
   return (
     <article className="pn-note-article">
-      <Link to="/" className="btn ghost pn-note-back">
-        <ArrowLeft size={14} />返回首页
-      </Link>
+      <Button type="text" size="small" className="pn-note-back" icon={<ArrowLeft size={14} />} onClick={() => navigate('/')}>
+        返回首页
+      </Button>
 
       {privatePreview && authenticated && (
-        <div className="pn-note-private" role="note">
-          <Eye size={15} />
-          私有预览：此笔记未公开，仅管理员可见
-        </div>
+        <Alert
+          role="note"
+          type="info"
+          showIcon={false}
+          className="pn-note-preview-alert"
+          message={
+            <>
+              <Eye size={15} />
+              私有预览：此笔记未公开，仅管理员可见
+            </>
+          }
+        />
       )}
 
       <h1 className="pn-note-title">{note.title}</h1>
@@ -57,7 +69,9 @@ export default function Note() {
           <>
             <span className="pn-note-meta-sep">·</span>
             {note.tags.map((t) => (
-              <Link key={t} to={`/tags/${encodeURIComponent(t)}`} className="pn-note-tag">{t}</Link>
+              <Tag key={t}>
+                <Link className="pn-tag-link" to={`/tags/${encodeURIComponent(t)}`}>{t}</Link>
+              </Tag>
             ))}
           </>
         )}
@@ -67,17 +81,21 @@ export default function Note() {
 
       <nav className="pn-note-postnav" aria-label="笔记导航">
         {note.prev ? (
-          <Link to={`/notes/${encodeURIComponent(note.prev.slug)}`} className="card pn-note-nav-card">
-            <span className="pn-note-nav-label"><ArrowLeft size={14} />上一篇</span>
-            <span className="pn-note-nav-title">{note.prev.title}</span>
+          <Link to={`/notes/${encodeURIComponent(note.prev.slug)}`} className="pn-note-nav-link">
+            <Card className="pn-note-nav-card" styles={{ body: { padding: 0 } }}>
+              <span className="pn-note-nav-label"><ArrowLeft size={14} />上一篇</span>
+              <span className="pn-note-nav-title">{note.prev.title}</span>
+            </Card>
           </Link>
         ) : (
           <span />
         )}
         {note.next ? (
-          <Link to={`/notes/${encodeURIComponent(note.next.slug)}`} className="card pn-note-nav-card pn-note-nav-next">
-            <span className="pn-note-nav-label">下一篇<ArrowRight size={14} /></span>
-            <span className="pn-note-nav-title">{note.next.title}</span>
+          <Link to={`/notes/${encodeURIComponent(note.next.slug)}`} className="pn-note-nav-link">
+            <Card className="pn-note-nav-card pn-note-nav-next" styles={{ body: { padding: 0 } }}>
+              <span className="pn-note-nav-label">下一篇<ArrowRight size={14} /></span>
+              <span className="pn-note-nav-title">{note.next.title}</span>
+            </Card>
           </Link>
         ) : (
           <span />