chore(lint): unify formatting on golangci-lint fmt (gofumpt), uncap issue reporting, fix gofumpt drift

- make format 现在与 code-check 使用同一格式化器（golangci-lint fmt），消除 goimports -local 与 gofumpt 的格式拉锯
- .golangci.yml 关闭默认 50/3 截断，完整上报所有问题（只增强不弱化）
- 全库 gofumpt 规范化（203 files, 纯格式无行为变更）

backend/core/extpoints/router.go

@@ -21,7 +21,7 @@ type RouteDefinition struct {
 type RouterExtension interface {
 	Use(middlewares ...any)
 	Group(prefix string, middlewares ...any) RouterExtension
-	Handle(method string, path string, handlers ...any) RouteDefinition
+	Handle(method, path string, handlers ...any) RouteDefinition
 	GET(path string, handlers ...any) RouteDefinition
 	POST(path string, handlers ...any) RouteDefinition
 	PUT(path string, handlers ...any) RouteDefinition