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/local.php.example

@@ -0,0 +1,57 @@
+<?php
+// 本地开发 / 默认值。生产请复制为 local.php 并填入真实密钥。
+return [
+    'app' => [
+        'env' => 'production',
+        'debug' => false,
+        'timezone' => 'Asia/Shanghai',
+        'jwt_secret' => 'CHANGE-ME-32CHARS-MINIMUM-SECRET',
+        'jwt_ttl' => 3600,
+        'jwt_refresh_ttl' => 2592000,
+        'cors_origins' => [
+            'https://design.cardsoon.com',
+        ],
+    ],
+    'db' => [
+        'host' => '127.0.0.1',
+        'port' => 3306,
+        'name' => 'soondesign',
+        'user' => 'soondesign',
+        'pass' => 'CHANGE-ME',
+        'charset' => 'utf8mb4',
+    ],
+    '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',
+        'models_dir' => '/www/wwwroot/design.cardsoon.com/soonModels',
+    ],
+    'limits' => [
+        'free_quota_mb' => 20,
+        'preview_require_membership' => true,
+        'member_quota_mb' => 2048,
+        'member_max_files' => 200,
+    ],
+    'rate_limits' => [
+        'admin/*' => ['capacity' => 120, 'window' => 60],
+        'POST /api/v1/auth/login' => ['capacity' => 10, 'window' => 60],
+        'POST /api/v1/auth/register' => ['capacity' => 5, 'window' => 60],
+        'POST /api/v1/files' => ['capacity' => 30, 'window' => 60],
+    ],
+    'alipay' => [
+        'app_id' => '',
+        'private_key' => '',
+        'public_key' => '',
+        'sandbox' => false,
+    ],
+    'wechat' => [
+        'app_id' => '',
+        'mch_id' => '',
+        'mch_serial_no' => '',
+        'mch_private_key' => '',
+        'api_v3_key' => '',
+        'sandbox' => false,
+    ],
+];