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>

preload.js

@@ -0,0 +1,39 @@
+const { contextBridge, ipcRenderer } = require('electron');
+
+contextBridge.exposeInMainWorld('api', {
+  sources: {
+    list: () => ipcRenderer.invoke('sources:list'),
+    browse: (sourceId, page) => ipcRenderer.invoke('source:list', sourceId, page),
+    search: (sourceId, keyword, page) => ipcRenderer.invoke('source:search', sourceId, keyword, page),
+    detail: (sourceId, postId) => ipcRenderer.invoke('source:detail', sourceId, postId),
+    download: (sourceId, postId) => ipcRenderer.invoke('source:download', sourceId, postId)
+  },
+  library: {
+    list: () => ipcRenderer.invoke('library:list'),
+    get: (id) => ipcRenderer.invoke('library:get', id),
+    findBySource: (sourceId, postId) => ipcRenderer.invoke('library:findBySource', sourceId, postId),
+    add: (item) => ipcRenderer.invoke('library:add', item),
+    update: (id, patch) => ipcRenderer.invoke('library:update', id, patch),
+    remove: (id, deleteFiles) => ipcRenderer.invoke('library:remove', id, deleteFiles),
+    onChanged: (cb) => ipcRenderer.on('library:changed', () => cb())
+  },
+  downloadFile: (url, suggestName, entryId, extraHeaders) => ipcRenderer.invoke('download:file', url, suggestName, entryId, extraHeaders),
+  zlib: {
+    hasCreds: () => ipcRenderer.invoke('zlib:hasCreds'),
+    login: (email, password) => ipcRenderer.invoke('zlib:login', email, password),
+    logout: () => ipcRenderer.invoke('zlib:logout')
+  },
+  proxy: {
+    get: () => ipcRenderer.invoke('proxy:get'),
+    set: (url) => ipcRenderer.invoke('proxy:set', url)
+  },
+  pickFile: () => ipcRenderer.invoke('dialog:pickFile'),
+  openPath: (p) => ipcRenderer.invoke('shell:openPath', p),
+  showItem: (p) => ipcRenderer.invoke('shell:showItem', p),
+  openExternal: (url) => ipcRenderer.invoke('shell:openExternal', url),
+  copy: (text) => ipcRenderer.invoke('copy', text),
+  getVersion: () => ipcRenderer.invoke('app:version'),
+  minimize: () => ipcRenderer.send('win:minimize'),
+  maximize: () => ipcRenderer.send('win:maximize'),
+  close: () => ipcRenderer.send('win:close')
+});