refactor(core): decouple gin from pkg/util and reduce code duplication

backend/pkg/util/gin_context.go

@@ -1,22 +0,0 @@
-// Copyright 2026 Arctel.net
-// SPDX-License-Identifier: Apache-2.0
-
-package util
-
-import "github.com/gin-gonic/gin"
-
-// GetFromContext retrieves a typed value from Gin context.
-func GetFromContext[T any](c *gin.Context, key string) (T, bool) {
-	value, exists := c.Get(key)
-	if !exists {
-		var zero T
-		return zero, false
-	}
-	typed, ok := value.(T)
-	return typed, ok
-}
-
-// SetToContext sets a typed value into Gin context.
-func SetToContext[T any](c *gin.Context, key string, value T) {
-	c.Set(key, value)
-}