feat: PeopleLib 开放文献客户端，集成 Z-Library 与 LibGen 等多源检索

Electron 桌面客户端，聚合多个开放获取文献源的搜索、详情与下载。

新增数据源：
- Z-Library：邮箱登录（凭据本地存储），会话失效自动重登
- LibGen：适配新版 libgen.ac 前端（旧版 search.php 镜像已全部下线）
- Memory of the World、Sci-Hub、Anna's Archive

基础设施：
- mirror.js：镜像故障转移，支持串行优先与并发竞速两种策略，
  失效镜像 5 分钟冷却后自动重试，避免站点恢复后被永久跳过
- http.js：统一 15 秒请求超时，防止单个卡死镜像拖垮整次搜索
- settings.js：全局代理配置持久化，经 Electron net.fetch 生效于所有请求

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/ui/app.js

@@ -0,0 +1,102 @@
+$('minBtn').onclick = () => window.api.minimize();
+$('maxBtn').onclick = () => window.api.maximize();
+$('closeBtn').onclick = () => window.api.close();
+
+let currentTab = 'library';
+
+function switchTab(tab) {
+  currentTab = tab;
+  document.querySelectorAll('.tab').forEach((t) => t.classList.toggle('active', t.dataset.tab === tab));
+  $('libraryTab').classList.toggle('hidden', tab !== 'library');
+  $('browseTab').classList.toggle('hidden', tab !== 'browse');
+  $('settingsTab').classList.toggle('hidden', tab !== 'settings');
+  if (tab === 'library') Library.refresh(true);
+}
+
+document.querySelectorAll('.tab').forEach((t) => {
+  t.onclick = () => switchTab(t.dataset.tab);
+});
+
+Browse.init();
+Library.init();
+
+const sortSelect = $('sortSelect');
+sortSelect.value = Library.getSortMode();
+sortSelect.onchange = () => Library.setSortMode(sortSelect.value);
+
+async function initSourceManager() {
+  const listEl = $('sourceList');
+  const res = await window.api.sources.list();
+  const all = res.ok ? res.data : [];
+  const enabled = getEnabledSources();
+  listEl.innerHTML = all.map((s) => {
+    const checked = enabled ? enabled.includes(s.id) : true;
+    return `
+    <label class="source-row">
+      <input type="checkbox" data-id="${escapeHtml(s.id)}" ${checked ? 'checked' : ''} />
+      <span>${escapeHtml(s.name)}</span>
+    </label>`;
+  }).join('');
+  listEl.querySelectorAll('input[type="checkbox"]').forEach((cb) => {
+    cb.onchange = () => {
+      const ids = Array.from(listEl.querySelectorAll('input[type="checkbox"]:checked'))
+        .map((el) => el.dataset.id);
+      setEnabledSources(ids);
+      Browse.reloadSources();
+    };
+  });
+}
+initSourceManager();
+
+async function refreshZlibStatus() {
+  const r = await window.api.zlib.hasCreds();
+  const logged = r.ok && r.data;
+  $('zlibStatus').textContent = logged ? '已配置（凭据保存在本地）' : '未登录';
+  $('zlibLoginBtn').textContent = logged ? '重新登录' : '登录';
+  $('zlibLogoutBtn').classList.toggle('hidden', !logged);
+}
+
+$('zlibLoginBtn').onclick = async () => {
+  const r = await openModal('Z-Library 登录', `
+    <p style="margin-bottom:8px;">使用 Z-Library 账号登录（保存在本地 userData 目录）</p>
+    <div style="display:flex;flex-direction:column;gap:8px;">
+      <input id="zlibEmail" type="email" placeholder="邮箱" style="padding:8px;background:#222;border:1px solid #444;color:#eee;border-radius:4px;" />
+      <input id="zlibPassword" type="password" placeholder="密码" style="padding:8px;background:#222;border:1px solid #444;color:#eee;border-radius:4px;" />
+      <div id="zlibErr" style="color:#f66;font-size:12px;min-height:16px;"></div>
+    </div>
+  `, async () => {
+    const email = $('zlibEmail').value.trim();
+    const password = $('zlibPassword').value;
+    if (!email || !password) { $('zlibErr').textContent = '请输入邮箱和密码'; return false; }
+    $('zlibErr').textContent = '登录中...';
+    const res = await window.api.zlib.login(email, password);
+    if (!res.ok) { $('zlibErr').textContent = res.error || '登录失败'; return false; }
+    if (res.data && res.data.ok === false) { $('zlibErr').textContent = res.data.error || '登录失败'; return false; }
+    return true;
+  });
+  if (r) refreshZlibStatus();
+};
+
+$('zlibLogoutBtn').onclick = async () => {
+  const ok = await confirmModal('退出 Z-Library', '确定要清除本地保存的 Z-Library 凭据吗？');
+  if (ok) { await window.api.zlib.logout(); refreshZlibStatus(); }
+};
+
+refreshZlibStatus();
+
+async function refreshProxy() {
+  const r = await window.api.proxy.get();
+  if (r.ok) $('proxyInput').value = r.data || '';
+}
+$('proxySaveBtn').onclick = async () => {
+  await window.api.proxy.set($('proxyInput').value.trim());
+  $('proxySaveBtn').textContent = '已保存 ✓';
+  setTimeout(() => { $('proxySaveBtn').textContent = '保存'; }, 1500);
+};
+refreshProxy();
+
+window.api.getVersion().then((r) => {
+  if (r && r.ok) $('appVersion').textContent = 'v' + r.data;
+});
+
+switchTab('library');