[NYC] Fix brocken file backoffice display

[BarbaraOliveira13]

🎩 Description

In the NYC plateform, the “Type” column in the attachments table displayed full AWS S3 URLs with query parameters (e.g. response-content-type=image%2fjpeg...) instead of the actual MIME type (JPEG, PDF, etc.).

Solution (instead of passing by AWS who will work after passing on decidim_app):
Patched the Decidim::Attachment model to redefine the file_type method.
The method now reads the MIME type directly from ActiveStorage::Blob#content_type instead of parsing the file URL.
Updated application.rb to ensure manual loading of decorators after initialization.

Result:
File types in the admin attachments table now display clean values (JPEG, PDF, etc.) even for long, signed AWS URLs.

Testing

1. Need to test in production !
2. Log in as an admin and open any participatory process.
3. Go to Process → Attachments.
4. Verify that the “Type” column shows clean MIME types (JPEG, PDF, etc.) instead of S3 URLs with parameters. 🎉

📌 Related Issues

Link your PR to an issue
https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?filterQuery=nyc&pane=issue&itemId=144569396&issue=OpenSourcePolitics%7Cintern-tasks%7C292&visibleFields=%5B%22Title%22%2C%22Assignees%22%2C%22Status%22%2C72184574%2C%22Linked+pull+requests%22%2C%22Labels%22%2C%22Repository%22%5D

OpenSourcePolitics/intern-tasks/issues/292

Tasks

• Add specs
• Add note about overrides in OVERLOADS.md
• In case of new dependencies or version bump, update related documentation

📷 Screenshots

Extra information