feat(attach): 附件可配置限额、流式落盘与分阶段上传

管理端可配类型/体积；上传改流式避免整文件进内存；发帖先选再传并拦截未上传提交；提高 Next proxy 体积上限。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/router/router.go

@@ -23,6 +23,8 @@ func Setup(cfg *config.Config) (*gin.Engine, error) {
 	}
 
 	r := gin.New()
+	// 大附件落盘到临时文件，避免 multipart 整文件进内存（默认 32MiB）
+	r.MaxMultipartMemory = 4 << 20
 	r.Use(gin.Recovery())
 	r.Use(gin.Logger())
 
@@ -49,8 +51,8 @@ func Setup(cfg *config.Config) (*gin.Engine, error) {
 	overviewSvc := service.NewOverviewService(model.DB)
 	checkinSvc := service.NewCheckinService(model.DB)
 	announcementSvc := service.NewAnnouncementService(model.DB)
-	uploadSvc := service.NewUploadService(model.DB, filepath.Join(cfg.DataDir, "uploads"))
-	postFileSvc := service.NewPostFileService(model.DB, filepath.Join(cfg.DataDir, "private"))
+	uploadSvc := service.NewUploadService(model.DB, filepath.Join(cfg.DataDir, "uploads")).WithSetting(settingSvc)
+	postFileSvc := service.NewPostFileService(model.DB, filepath.Join(cfg.DataDir, "private")).WithSetting(settingSvc)
 	pointsSvc := service.NewPointsService(model.DB)
 	adminUserSvc := service.NewAdminUserService(model.DB)
 	moderationSvc := service.NewModerationService(model.DB, notifSvc)