chore: remove direct avatar upload endpoint (POST /profile/avatar);

feat: add endpoints for presigned upload URLs (GET /upload/avatar, GET /upload/image);
refactor: replace ProfileDto with NewProfileDto in update profile endpoint;
feat: implement S3 integration for avatar management;
fix: update database queries to handle new avatar upload flow;
chore: add new dependencies for S3 handling (golang.org/x/time);
refactor: rename UploadService to S3Service;
refactor: change return type for func LocalizeS3Url(originalURL string) (*url.URL, error);
feat: add custom validator for upload_id

backend/internal/models/s3.go

@@ -0,0 +1,24 @@
+// 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 models
+
+type PresignedUploadResponse struct {
+	Url    string            `json:"url"`
+	Fields map[string]string `json:"fields"`
+}
+