fix: use relative URLs for CKEditor uploaded image responses

[Neophytis]

Problem

GalleryController::uploadImageCkeditor() returns an absolute URL when responding to CKEditor after an image upload:

'url' => $this->generateUrl(
    'gallery_uploaded_ckeditor',
    ['id' => ..., 'fileInfo' => ...],
    UrlGeneratorInterface::ABSOLUTE_URL   // ← hardcoded to production domain
),

CKEditor embeds this URL directly into the post HTML as an <img src="...">. Because the URL is absolute (https://bewelcome.org/...), images uploaded on production are broken when the same post is viewed on stage.bewelcome.org or any other domain — the browser fetches from bewelcome.org, which requires authentication there.

Fix

Change ABSOLUTE_URL to RELATIVE_PATH (Symfony default) so the embedded URL is /gallery/show/uploaded/{id}/{fileInfo}, which resolves against whatever domain the post is viewed on.

File: src/Controller/GalleryController.php
Change: UrlGeneratorInterface::ABSOLUTE_URL → UrlGeneratorInterface::RELATIVE_PATH

Impact

• Newly uploaded images will display correctly on stage.bewelcome.org and any other environment
• Existing posts with hardcoded https://bewelcome.org/... URLs are not retroactively fixed
• The /gallery/show/uploaded route still requires authentication — no change to access control