refactor(skydive): replace MongoDB User with MySQL UserService

All skydive routes now fetch users via UserService (MySQL) instead of
mongoose.model('User'). Key changes:
- user._id.toString() → user.id (same UUID, different source)
- User.findOne({ username }) → UserService.getUserByUsername()
- /feed route migrated to async/await using UserService.getUserFollowed()
  to resolve the following list from the MySQL Follower table
- jump/file/application author set as user.id (UUID string) instead of
  the full Mongoose document
- jump.toJSONFor(null) — following field in responses is now always false
  until Jump model is migrated away from MongoDB User dependency
- user.controller: licence/poids/bg_image routed to SkydiverProfileService
  fixing the silent Sequelize save bug for those fields

src/controllers/user.controller.js

@@ -1,4 +1,4 @@
-const { UserService } = require('../services');
+const { UserService, SkydiverProfileService } = require('../services');
 const asyncHandler = require("../middlewares/asyncHandler");
 const ErrorResponse = require("../utils/errorResponse");
 var crypto = require('crypto');
@@ -129,33 +129,26 @@ module.exports.updateUser = asyncHandler(async (req, res, next) => {
         if (typeof req.body.user.phone !== 'undefined') {
             user.phone = req.body.user.phone;
         }
-        if (typeof req.body.user.licence !== 'undefined') {
-            user.licence = req.body.user.licence;
-        }
-        if (typeof req.body.user.poids !== 'undefined') {
-            user.poids = req.body.user.poids;
-        }
         if (typeof req.body.user.image !== 'undefined') {
             user.image = req.body.user.image;
         }
-        if (typeof req.body.user.bg_image !== 'undefined') {
-            user.bg_image = req.body.user.bg_image;
-        }
         if (typeof req.body.user.role !== 'undefined') {
             return next(new ErrorResponse("Forbidden", 403, "A suspected attempt to usurp rights has been detected. The suspicious activity has been reported and xill be investigated."));
         }
 
-        // Persist changes using the service (service will save instance or update+fetch)
         const updatedUser = await UserService.updateUserById(user, req.payload.id);
+
+        const skydiverFields = {};
+        if (typeof req.body.user.licence !== 'undefined') skydiverFields.licence = req.body.user.licence;
+        if (typeof req.body.user.poids !== 'undefined') skydiverFields.poids = req.body.user.poids;
+        if (typeof req.body.user.bg_image !== 'undefined') skydiverFields.bg_image = req.body.user.bg_image;
+        if (Object.keys(skydiverFields).length > 0) {
+            await SkydiverProfileService.upsert(req.payload.id, skydiverFields);
+        }
+
         res.status(200).json({
             user: updatedUser.toAuthJSON()
         });
-        /*return user.save().then(function () {
-            return res.json({
-                    message: 'User updated successfully.',
-                    user: user.toAuthJSON()
-                });
-        });*/
     } catch (err) {
         return next(new ErrorResponse('Something went wrong while updating user.', 500, err.message));
     }