refactor: introduce DTOs for claims, session, and request handling

feat: add token validation service method
refactor: update middleware to use structured DTOs
feat: implement session info propagation through context
refactor: replace ad-hoc structs with DTOs in middleware
chore: organize auth-related data structures

backend/internal/utils/request.go

@@ -1,32 +1,31 @@
 // Copyright (c) 2025 Nikolai Papin
-// 
+//
 // This file is part of Easywish
-// 
+//
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
-// 
+//
 // This program is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 // the GNU General Public License for more details.
-// 
+//
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 package utils
 
 import (
-	"easywish/internal/middleware"
-
+	"easywish/internal/dto"
 	"github.com/gin-gonic/gin"
 )
 
-func GetRequest[T any](c *gin.Context) (*middleware.Request[T], bool) {
+func GetRequest[T any](c *gin.Context) (*dto.Request[T], bool) {
 
 	req, ok := c.Get("request")
-	request := req.(middleware.Request[T])
+	request := req.(dto.Request[T])
 	if !ok {
 		return nil, false
 	}