feat(auth): 添加用户注册开关功能

- 在系统设置中新增 allowRegister 配置项控制用户注册
- 实现注册接口的开关检查机制
- 登录页面根据注册开关动态显示或隐藏注册选项
- 首次 Linux.do 登录创建用户时也受注册开关限制
- 更新系统配置文档说明新的认证配置项

service/auth.go

@@ -59,6 +59,14 @@ func EnsureDefaultAdmin() error {
 }
 
 func Register(username string, password string) (model.AuthSession, error) {
+	settings, err := repository.GetSettings()
+	if err != nil {
+		return model.AuthSession{}, err
+	}
+	normalizedSettings := normalizeSettings(settings)
+	if normalizedSettings.Public.Auth.AllowRegister != nil && !*normalizedSettings.Public.Auth.AllowRegister {
+		return model.AuthSession{}, safeMessageError{message: "当前未开放注册"}
+	}
 	username = strings.TrimSpace(username)
 	if strings.ContainsAny(username, " \t\r\n") {
 		return model.AuthSession{}, safeMessageError{message: "用户名不能包含空格"}
@@ -163,6 +171,9 @@ func LoginWithLinuxDo(r *http.Request, code string, state string) (model.AuthSes
 		return model.AuthSession{}, redirect, err
 	}
 	if !ok {
+		if settings.Public.Auth.AllowRegister != nil && !*settings.Public.Auth.AllowRegister {
+			return model.AuthSession{}, redirect, safeMessageError{message: "当前未开放注册"}
+		}
 		user = model.User{
 			ID:          newID("user"),
 			Username:    linuxDoUsername(profile.Username, linuxDoID),

service/settings.go

@@ -78,6 +78,10 @@ func normalizePublicSetting(setting model.PublicSetting) model.PublicSetting {
 		enabled := true
 		setting.ModelChannel.AllowCustomChannel = &enabled
 	}
+	if setting.Auth.AllowRegister == nil {
+		enabled := true
+		setting.Auth.AllowRegister = &enabled
+	}
 	return setting
 }