feat: site management + cross-site torrent search

Port the complete site management system from the original MediaStation:

Model:
  - model/model.go: Added Site table with fields for name, base_url,
    site_type (nexusphp/gazelle/unit3d/mteam/custom_rss), auth_type
    (cookie/api_key/authorization), cookie, api_key, auth_header,
    user_agent, rss_url, timeout, priority, use_proxy, enabled,
    login_status, downloader. Registered in AllModels().

Backend services:
  - service/site.go: SiteService with CRUD (Create/List/FindByID/Update/
    Delete), TestConnection (validates credentials via HTTP, updates
    login_status in DB), and Search (cross-site fan-out that queries
    every enabled site adapter and returns merged results sorted by
    seeders descending).
  - service/site_adapter.go: SiteAdapter interface + NewSiteAdapter
    factory + 5 implementations:
    * nexusPhpAdapter — regex HTML scraping of torrents.php
    * gazelleAdapter — JSON API /ajax.php?action=browse
    * unit3dAdapter — REST API /api/torrents/filter
    * mteamAdapter — M-Team v3 POST /api/torrent/search with x-api-key
    * rssAdapter — XML RSS/Atom feed parsing with keyword filter

Handler + routes:
  - handler/sites.go: listSites, getSite, createSite, updateSite,
    deleteSite, testSite, siteSearch handlers.
  - handler/handler.go: 7 new routes under authed group:
    GET/POST /sites, GET/PUT/DELETE /sites/:id,
    POST /sites/:id/test, GET /sites/search.

Frontend:
  - api/sites.ts: typed interfaces (Site, SiteSearchResult,
    CreateSiteInput) and sitesAPI helper.
  - pages/SitesPage.tsx: full CRUD UI with add-site form (site_type +
    auth_type selectors, cookie/api_key/rss inputs), connection test
    button with live status indicator, delete action.
  - pages/SiteSearchPage.tsx: cross-site search with keyword input,
    merged result table (site/title/size/seeders/leechers/free),
    one-click download-to-qBittorrent button.
  - App.tsx: lazy-loaded routes /sites and /site-search.
  - Layout.tsx: sidebar links 站点管理 + 站点搜索 under 自动化 group.

Verified: go build + go vet + go test pass; tsc -b + vite build passes
(32 lazy chunks, main bundle 255 KB / 85 KB gzipped).

web/src/pages/SiteSearchPage.tsx

@@ -0,0 +1,161 @@
+import { FormEvent, useState } from 'react'
+import toast from 'react-hot-toast'
+import { Download, Search } from 'lucide-react'
+
+import { sitesAPI, type SiteSearchResult } from '../api/sites'
+import { downloadsAPI } from '../api/downloads'
+
+function fmtBytes(n: number): string {
+  if (!n || n <= 0) return '—'
+  const u = ['B', 'KB', 'MB', 'GB', 'TB']
+  let v = n
+  let i = 0
+  while (v >= 1024 && i < u.length - 1) {
+    v /= 1024
+    i++
+  }
+  return `${v.toFixed(1)} ${u[i]}`
+}
+
+// SiteSearchPage performs cross-site torrent search across all enabled
+// sites and displays a merged result table sorted by seeders.
+export function SiteSearchPage() {
+  const [keyword, setKeyword] = useState('')
+  const [results, setResults] = useState<SiteSearchResult[]>([])
+  const [loading, setLoading] = useState(false)
+  const [searched, setSearched] = useState(false)
+
+  const onSubmit = async (e: FormEvent) => {
+    e.preventDefault()
+    if (!keyword.trim()) return
+    setLoading(true)
+    setSearched(true)
+    try {
+      const data = await sitesAPI.search(keyword.trim())
+      setResults(data.items || [])
+      if ((data.items || []).length === 0) {
+        toast('未找到结果,请检查站点配置或更换关键词')
+      }
+    } catch (err: unknown) {
+      const msg =
+        (err as { response?: { data?: { error?: string } } })?.response?.data?.error ??
+        '搜索失败'
+      toast.error(msg)
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  const downloadTorrent = async (item: SiteSearchResult) => {
+    const url = item.download_url || item.torrent_url
+    if (!url) {
+      toast.error('无可用下载链接')
+      return
+    }
+    try {
+      await downloadsAPI.add(url)
+      toast.success(`已加入下载: ${item.title.substring(0, 40)}...`)
+    } catch (err: unknown) {
+      const msg =
+        (err as { response?: { data?: { error?: string } } })?.response?.data?.error ??
+        '下载失败'
+      toast.error(msg)
+    }
+  }
+
+  return (
+    <div className="space-y-6">
+      <header className="flex items-center gap-3">
+        <Search className="h-6 w-6 text-primary-400" />
+        <div>
+          <h1 className="font-display text-3xl font-bold text-white">站点搜索</h1>
+          <p className="text-sm text-slate-400">
+            跨站搜索所有已启用的 PT/BT 站点,结果按做种数排序。
+          </p>
+        </div>
+      </header>
+
+      <form onSubmit={onSubmit} className="flex gap-2">
+        <input
+          autoFocus
+          className="input-base flex-1"
+          placeholder="输入关键词搜索(如: 流浪地球 / Dune 2024)"
+          value={keyword}
+          onChange={(e) => setKeyword(e.target.value)}
+        />
+        <button type="submit" disabled={loading} className="neon-button">
+          {loading ? '搜索中…' : '搜索'}
+        </button>
+      </form>
+
+      {loading && <p className="text-slate-500">正在查询所有站点…</p>}
+
+      {!loading && searched && results.length === 0 && (
+        <div className="glass-panel">
+          <p className="text-slate-300">
+            未找到结果。请确认已在「站点管理」中添加并启用了至少一个站点,且 Cookie / API Key 有效。
+          </p>
+        </div>
+      )}
+
+      {results.length > 0 && (
+        <div className="glass-panel overflow-x-auto">
+          <table className="w-full text-left text-sm">
+            <thead className="text-xs uppercase tracking-wider text-slate-500">
+              <tr>
+                <th className="py-2">站点</th>
+                <th>标题</th>
+                <th>大小</th>
+                <th>S</th>
+                <th>L</th>
+                <th>Free</th>
+                <th className="text-right">操作</th>
+              </tr>
+            </thead>
+            <tbody>
+              {results.map((item, idx) => (
+                <tr key={idx} className="border-t border-white/5 align-top">
+                  <td className="py-2 text-primary-400">{item.site_name}</td>
+                  <td className="max-w-md py-2">
+                    <a
+                      href={item.torrent_url}
+                      target="_blank"
+                      rel="noopener noreferrer"
+                      className="text-white transition hover:text-primary-400"
+                      title={item.title}
+                    >
+                      {item.title.length > 80
+                        ? item.title.substring(0, 80) + '…'
+                        : item.title}
+                    </a>
+                  </td>
+                  <td className="whitespace-nowrap text-slate-300">
+                    {fmtBytes(item.size)}
+                  </td>
+                  <td className="text-emerald-400">{item.seeders || '—'}</td>
+                  <td className="text-red-400">{item.leechers || '—'}</td>
+                  <td>
+                    {item.free && (
+                      <span className="rounded border border-emerald-400/40 px-1.5 py-0.5 text-xs text-emerald-400">
+                        Free
+                      </span>
+                    )}
+                  </td>
+                  <td className="py-2 text-right">
+                    <button
+                      onClick={() => downloadTorrent(item)}
+                      className="rounded border border-primary-400/40 px-2 py-1 text-xs text-primary-400 hover:bg-primary-400/10"
+                      title="加入下载"
+                    >
+                      <Download size={12} className="inline" />
+                    </button>
+                  </td>
+                </tr>
+              ))}
+            </tbody>
+          </table>
+        </div>
+      )}
+    </div>
+  )
+}