重构 monorepo 并完善网页端订阅与首页体验

- 迁移为 frontend-web、frontend-electron、backend-web 与 docker 部署结构
- 网页端：订阅门禁二次弹窗、套餐/支付组件化、顶栏分组对齐
- 首页：最近文件与模板库布局优化，缩略图对齐，下载与删除操作
- 新增管理后台、支付与云端文件 API，更新 README 与项目规范

Co-authored-by: Cursor <cursoragent@cursor.com>

backend-web/config/config.designadmin.cardsoon.example.php

@@ -0,0 +1,25 @@
+<?php
+// designadmin.cardsoon.com (后端) — 在宝塔站点根目录把此文件复制为 local.php 后修改密钥。
+return [
+    'app' => [
+        'env' => 'production',
+        'debug' => false,
+        'cors_origins' => [
+            'https://design.cardsoon.com',
+        ],
+    ],
+    'db' => [
+        'host' => '127.0.0.1',
+        'port' => 3306,
+        'name' => 'soondesign',
+        'user' => 'soondesign',
+        'pass' => 'CHANGE-ME',
+    ],
+    'site' => [
+        'base_url' => 'https://designadmin.cardsoon.com',
+        'front_base_url' => 'https://design.cardsoon.com',
+    ],
+    'storage' => [
+        'users_dir' => '/www/wwwroot/designadmin.cardsoon.com/backend/storage/users',
+    ],
+];