Raise upload limit to 8 MB

- docker/php/php.ini: upload_max_filesize 8M / post_max_size 10M
- docker/nginx/default.conf: client_max_body_size 10M
- ArtworkType: Image maxSize 8M with a clear message + help text

(local C:\php\php.ini was bumped from 2M the same way — not in the repo)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/Form/ArtworkType.php

@@ -22,12 +22,14 @@ class ArtworkType extends AbstractType
             ->add('file', FileType::class, [
                 'label' => 'Image file',
                 'mapped' => false,
+                'help' => 'PNG, JPEG, GIF or WebP, up to 8 MB.',
                 'constraints' => [
                     new NotNull(message: 'Please choose an image.'),
                     new Image(
-                        maxSize: '20M',
+                        maxSize: '8M',
                         mimeTypes: ['image/png', 'image/jpeg', 'image/gif', 'image/webp'],
                         mimeTypesMessage: 'Upload a PNG, JPEG, GIF or WebP image.',
+                        maxSizeMessage: 'The image is too large ({{ size }} {{ suffix }}). Max is 8 MB.',
                     ),
                 ],
             ]);