fun: add BindRoute for custom HTTP routes (GET/POST, form-data callbacks)

- BindRoute(method, path, handler) with exact-match routing dispatched before /cell RPC
- RouteCtx merges query args and form-urlencoded POST args for callback scenarios (e.g. epay notify)
- handler returns error -> unified Result error response; nil -> full control via fasthttp.RequestCtx (plain-text 'success' replies)
- /cell reserved; duplicate/invalid registration panics at startup; all existing tests pass

fun.go

@@ -10,9 +10,10 @@ import (
 
 type Fun struct {
 	methods       map[string]methodInfo
-	boxes         *sync.Map         // 依赖容器：reflect.Type → reflect.Value
-	guards        []*any            // 全局 Guard
-	serviceGuards map[string][]*any // 服务级 Guard，按服务名
+	routes        map[string]RouteHandler // 自定义路由："GET /path" → 处理器
+	boxes         *sync.Map              // 依赖容器：reflect.Type → reflect.Value
+	guards        []*any                 // 全局 Guard
+	serviceGuards map[string][]*any      // 服务级 Guard，按服务名
 }
 
 var (
@@ -33,6 +34,7 @@ type methodInfo struct {
 func New() *Fun {
 	f := &Fun{
 		methods:       map[string]methodInfo{},
+		routes:        map[string]RouteHandler{},
 		boxes:         &sync.Map{},
 		serviceGuards: map[string][]*any{},
 	}