fix: change avatar upload response to JSON object with URL;

feat: add UrlDto for standardized URL responses;
refactor: update avatar upload endpoint to return UrlDto;
docs: regenerate Swagger;
chore: add comments for untested profile controller methods

backend/internal/dto/general.go

@@ -0,0 +1,22 @@
+// 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 dto
+
+type UrlDto struct {
+	Url string `json:"url" binding:"required"`
+}