feat: PDF 转换前端（epub 上传/进度轮询/下载/用户软删，复用 zTools2 API）

便携式 Vue3 前端：上传 epub 转 PDF，显示上传与转换进度，完成后下载；
用户可软删任务（不再对自己展示，管理员仍可见）。凭 cookie 标识用户。
复用 zTools2 后端 /api/pdf/*（同源），独立 i18n（中英懒加载），
可独立运行或经 mainPage iframe 同源集成。含 vitest 单测 20 项。

src/i18n/locales/en.js

@@ -0,0 +1,41 @@
+// 英文语言包 -- 通过动态 import() 加载，被打成独立 chunk，
+// 只看中文的访客不会下载此文件。
+export default {
+  app: {
+    title: 'PDF Converter'
+  },
+  upload: {
+    hint: 'Drop an .epub file, or',
+    pick: 'click to choose',
+    limit: 'Only epub, up to 250MB',
+    requireEpub: 'Only epub files are supported',
+    oversize: 'File exceeds the 250MB limit',
+    uploading: 'Uploading…',
+    submitted: 'Submitted, converting…',
+    failed: 'Upload failed',
+    networkError: 'Network error'
+  },
+  list: {
+    count: '{total} task(s)',
+    empty: 'No tasks yet. Upload an epub to start.',
+    loading: 'Loading…',
+    loadFailed: 'Load failed: {msg}'
+  },
+  job: {
+    name: 'Filename',
+    size: 'Size',
+    status: 'Status',
+    created: 'Created',
+    actions: 'Actions',
+    statusDone: 'Done',
+    statusFailed: 'Failed',
+    statusConverting: 'Converting',
+    statusPending: 'Queued',
+    download: 'Download',
+    delete: 'Delete',
+    deleteConfirm: 'Delete "{name}"?\nIt will no longer be shown to you (admin can still see it; only admin hard-delete truly removes it).',
+    deleted: 'Deleted',
+    deleteFailed: 'Delete failed: {msg}'
+  },
+  refresh: 'Refresh'
+}