AO3-7473 Possible to upload unusable collection/skin icon

[cinderbrick1212]

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Issue

https://otwarchive.atlassian.net/browse/AO3-7473

Purpose

I updated the allowed image formats for Skin and Collection icons to prevent 500 errors.

Previously, the validation accepted any image/* MIME type, which caused server crashes when the image processing library attempted to resize unsupported vector formats like SVGs. I updated app/models/skin.rb and app/models/collection.rb to strictly allow image/gif, image/jpeg, and image/png, mirroring the safer validation that is already in place for Pseud icons.

Testing Instructions

1. Log in to the application.
2. Navigate to the page to create or edit a Collection.
3. Attempt to upload an .svg file (or another unsupported image format) as the icon and submit the form.
4. Verify that the upload is blocked and a standard validation error is displayed, rather than throwing a 500 error.
5. Repeat steps 2-4 for creating or editing a Skin.
6. Upload a valid .png, .jpg, or .gif to ensure standard uploads still process correctly for both models.

Credit

Anish Kapoor (he/him)

[Copilot]

Pull request overview

This PR prevents 500 errors during Skin/Collection icon processing by restricting icon uploads to raster image MIME types that the resizing pipeline can safely handle (GIF/JPEG/PNG), matching the existing Pseud icon validation approach.

Changes:

• Tightened Skin icon allowed_formats from any image/* MIME type to image/gif, image/jpeg, and image/png.
• Tightened Collection icon allowed_formats from any image/* MIME type to image/gif, image/jpeg, and image/png.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
app/models/skin.rb	Restricts Skin icon MIME types to GIF/JPEG/PNG to avoid unsupported formats causing processing errors.
app/models/collection.rb	Restricts Collection icon MIME types to GIF/JPEG/PNG to avoid unsupported formats causing processing errors.

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