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/docs/swagger.yaml

@@ -34,6 +34,13 @@ definitions:
       hide_profile_details:
         type: boolean
     type: object
+  dto.UrlDto:
+    properties:
+      url:
+        type: string
+    required:
+    - url
+    type: object
   models.ChangePasswordRequest:
     properties:
       old_password:
@@ -394,12 +401,12 @@ paths:
         required: true
         type: file
       produces:
-      - text/plain
+      - application/json
       responses:
         "200":
           description: Uploaded image url
           schema:
-            type: string
+            $ref: '#/definitions/dto.UrlDto'
       security:
       - JWT: []
       summary: Upload an avatar