fix: 添加缺失的USERNAME环境变量以修复500错误

- 在 wrangler.toml 中为生产和预览环境添加 USERNAME 变量
- USERNAME 用于站长用户身份验证和管理权限控制
- 修复因缺失 USERNAME 导致的管理后台无法访问问题
- 更新部署指南，添加详细的500错误故障排除方案
- 包含完整的环境变量检查清单和验证步骤

wrangler.toml

@@ -19,6 +19,7 @@ NEXT_PUBLIC_STORAGE_TYPE = "d1"
 NEXT_PUBLIC_SITE_NAME = "KatelyaTV"
 NEXT_PUBLIC_SITE_DESCRIPTION = "高性能影视播放平台"
 NEXTAUTH_URL = "https://your-domain.pages.dev"
+USERNAME = "katelya"
 IMAGE_PROXY_ENABLED = "true"
 CACHE_TTL = "3600"
 CORS_ORIGIN = "*"
@@ -45,5 +46,6 @@ database_id = "6d580637-1f87-4ddf-8b4d-3d97254b4c33"
 NEXT_PUBLIC_STORAGE_TYPE = "d1"
 NEXT_PUBLIC_SITE_NAME = "KatelyaTV"
 NEXT_PUBLIC_SITE_DESCRIPTION = "高性能影视播放平台"
+USERNAME = "katelya"
 IMAGE_PROXY_ENABLED = "true"
 NODE_ENV = "production"