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/library/store.js

@@ -0,0 +1,130 @@
+const { app } = require('electron');
+const fs = require('fs');
+const path = require('path');
+const { fetchWithProxy } = require('../sources/http');
+
+const DL_UA = 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36';
+
+const FILE = () => path.join(app.getPath('userData'), 'library.json');
+const COVER_DIR = () => path.join(app.getPath('userData'), 'covers');
+
+let items = null;
+let changeListener = null;
+
+function isRemoteCover(c) { return typeof c === 'string' && /^https?:\/\//i.test(c); }
+function coverExt(url) {
+  const m = String(url).split('?')[0].match(/\.(png|jpe?g|webp|gif|bmp)$/i);
+  return m ? m[0].toLowerCase() : '.img';
+}
+
+async function cacheCover(id, url) {
+  try {
+    const res = await fetchWithProxy(url, { headers: { 'User-Agent': DL_UA, 'Referer': new URL(url).origin } });
+    if (!res.ok) return '';
+    const buf = Buffer.from(await res.arrayBuffer());
+    if (!buf.length) return '';
+    fs.mkdirSync(COVER_DIR(), { recursive: true });
+    const dest = path.join(COVER_DIR(), id + coverExt(url));
+    fs.writeFileSync(dest, buf);
+    return dest;
+  } catch (e) { return ''; }
+}
+
+async function ensureCoverCached(id) {
+  const it = get(id);
+  if (!it || !isRemoteCover(it.cover)) return;
+  const local = await cacheCover(id, it.cover);
+  if (local && get(id)) { update(id, { cover: local }); notifyChange(); }
+}
+
+function removeCoverFile(id) {
+  try {
+    const dir = COVER_DIR();
+    if (!fs.existsSync(dir)) return;
+    for (const f of fs.readdirSync(dir)) {
+      if (f === id || f.startsWith(id + '.')) { try { fs.unlinkSync(path.join(dir, f)); } catch (e) { /* ignore */ } }
+    }
+  } catch (e) { /* ignore */ }
+}
+
+function setChangeListener(fn) { changeListener = typeof fn === 'function' ? fn : null; }
+function notifyChange() { if (changeListener) { try { changeListener(); } catch (e) { /* ignore */ } } }
+
+function load() {
+  if (items) return items;
+  try {
+    items = JSON.parse(fs.readFileSync(FILE(), 'utf-8'));
+    if (!Array.isArray(items)) items = [];
+  } catch (e) { items = []; }
+  return items;
+}
+
+function persist() {
+  fs.mkdirSync(path.dirname(FILE()), { recursive: true });
+  fs.writeFileSync(FILE(), JSON.stringify(items, null, 2), 'utf-8');
+}
+
+function genId() { return Date.now().toString(36) + Math.random().toString(36).slice(2, 8); }
+
+function list() {
+  return load().slice().sort((a, b) => (b.addedAt || 0) - (a.addedAt || 0));
+}
+
+function get(id) { return load().find((x) => x.id === id) || null; }
+
+function findBySource(sourceId, sourcePostId) {
+  return load().find((x) => x.sourceId === sourceId && String(x.sourcePostId) === String(sourcePostId)) || null;
+}
+
+function add(item) {
+  load();
+  const it = {
+    id: genId(),
+    title: item.title || '未命名',
+    authors: item.authors || [],
+    cover: item.cover || '',
+    date: item.date || '',
+    brief: item.brief || '',
+    url: item.url || '',
+    sourceId: item.sourceId || null,
+    sourcePostId: item.sourcePostId != null ? String(item.sourcePostId) : null,
+    files: item.files || [],        // [{ path, name, format }]
+    addedAt: Date.now()
+  };
+  items.push(it);
+  persist();
+  if (isRemoteCover(it.cover)) ensureCoverCached(it.id);
+  return it;
+}
+
+function update(id, patch) {
+  load();
+  const it = items.find((x) => x.id === id);
+  if (!it) throw new Error('条目不存在');
+  Object.assign(it, patch);
+  persist();
+  return it;
+}
+
+function attachFile(id, filePath) {
+  const it = get(id);
+  if (!it) return;
+  const files = (it.files || []).filter((f) => f.path !== filePath);
+  files.push({ path: filePath, name: path.basename(filePath), format: (path.extname(filePath) || '').slice(1).toUpperCase() });
+  update(id, { files });
+  notifyChange();
+}
+
+function remove(id, deleteFiles) {
+  load();
+  const it = get(id);
+  if (deleteFiles && it && it.files) {
+    for (const f of it.files) { try { if (f.path && fs.existsSync(f.path)) fs.unlinkSync(f.path); } catch (e) { /* ignore */ } }
+  }
+  items = items.filter((x) => x.id !== id);
+  persist();
+  removeCoverFile(id);
+  return { removed: true };
+}
+
+module.exports = { list, get, findBySource, add, update, remove, attachFile, setChangeListener };