refactor(auth): 将 Linux DO OAuth 配置迁移到系统设置

- 将 LinuxDo Connect 配置从环境变量迁移到数据库持久化
- 在管理后台系统设置中添加 LinuxDo OAuth 配置项
- 简化部署流程，无需修改 docker-compose.override.yml

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/cmd/server/wire_gen.go

@@ -53,7 +53,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	emailQueueService := service.ProvideEmailQueueService(emailService)
 	authService := service.NewAuthService(userRepository, configConfig, settingService, emailService, turnstileService, emailQueueService)
 	userService := service.NewUserService(userRepository)
-	authHandler := handler.NewAuthHandler(configConfig, authService, userService)
+	authHandler := handler.NewAuthHandler(configConfig, authService, userService, settingService)
 	userHandler := handler.NewUserHandler(userService)
 	apiKeyRepository := repository.NewAPIKeyRepository(client)
 	groupRepository := repository.NewGroupRepository(client, db)