feat(admin-v2): add Knowledge base management page

- 4 tabs: Items (CRUD + ProTable), Categories (tree management), Search, Analytics
- Knowledge service with full API integration
- Nav item + breadcrumb + route registration
- Analytics overview with 8 KPI statistics

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

admin-v2/src/layouts/AdminLayout.tsx

@@ -16,6 +16,7 @@ import {
   SunOutlined,
   MoonOutlined,
   ApiOutlined,
+  BookOutlined,
 } from '@ant-design/icons'
 import { Avatar, Dropdown, Tooltip, Drawer } from 'antd'
 import { useAuthStore } from '@/stores/authStore'
@@ -42,6 +43,7 @@ const navItems: NavItem[] = [
   { path: '/api-keys', name: 'API 密钥', icon: <ApiOutlined />, permission: 'provider:manage', group: '资源管理' },
   { path: '/usage', name: '用量统计', icon: <BarChartOutlined />, permission: 'admin:full', group: '运维' },
   { path: '/relay', name: '中转任务', icon: <SwapOutlined />, permission: 'relay:use', group: '运维' },
+  { path: '/knowledge', name: '知识库', icon: <BookOutlined />, permission: 'knowledge:read', group: '资源管理' },
   { path: '/logs', name: '操作日志', icon: <FileTextOutlined />, permission: 'admin:full', group: '运维' },
   { path: '/config', name: '系统配置', icon: <SettingOutlined />, permission: 'config:read', group: '系统' },
   { path: '/prompts', name: '提示词管理', icon: <MessageOutlined />, permission: 'prompt:read', group: '系统' },
@@ -204,6 +206,7 @@ const breadcrumbMap: Record<string, string> = {
   '/agent-templates': 'Agent 模板',
   '/usage': '用量统计',
   '/relay': '中转任务',
+  '/knowledge': '知识库',
   '/config': '系统配置',
   '/prompts': '提示词管理',
   '/logs': '操作日志',