feat: 文传易匿名临时文件传输站初始版本

- 后端 .NET 8 + FreeSql + 阿里云 OSS，支持共享/私密/标签三种文件模式
- 前端 Vue3 + Vite + TDesign，上传/取件/管理三页
- 取件码/二维码/海报合成（含保存二维码为图片）
- deploy/ 部署文档与一键 FTP 发布脚本
- appsettings.json 含真实凭据，已 gitignore 不入库

backend/WenChuanyi.Api/appsettings.example.json

@@ -0,0 +1,39 @@
+{
+  "App": {
+    "BaseUrl": "https://wenchuanyi.bbitcn.net"
+  },
+  "ConnectionStrings": {
+    "MySql": "Data Source=116.198.221.125;Port=3306;User ID=wenchuanyi;Password=YOUR_DB_PASSWORD;Initial Catalog=wenchuanyi;Charset=utf8mb4;SslMode=None;Allow User Variables=true;Treat Tiny As Boolean=true"
+  },
+  "Oss": {
+    "Endpoint": "oss-cn-chengdu.aliyuncs.com",
+    "STSEndpoint": "sts.cn-chengdu.aliyuncs.com",
+    "Bucket": "bbit-f8-web",
+    "AccessKeyId": "YOUR_ACCESS_KEY_ID",
+    "AccessKeySecret": "YOUR_ACCESS_KEY_SECRET",
+    "BaseKey": "文传易2026"
+  },
+  "OpenApi": {
+    "UploadRoot": "D:\\WenChuanyi\\UploadRoot"
+  },
+  "Cleaner": {
+    "IntervalMinutes": 30
+  },
+  "Kestrel": {
+    "Endpoints": {
+      "Http": {
+        "Url": "http://0.0.0.0:5280"
+      }
+    },
+    "Limits": {
+      "MaxRequestBodySize": 220200960
+    }
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  },
+  "AllowedHosts": "*"
+}