Binary attachment upload: Thumbnails for the attachments uploaded in SBL

**Functional architect/designer:** @-mention
**Technical architect:** @-mention

**Description**
Should there be thumbnails for the attachments uploaded with the Binary attachment upload?

- Possibility of Thumbnail / miniature image of attachment in SBL (like in Finder on Mac and Finn)
- Should the view of uploaded attachment be the same for all types for attachments and services? Many attachments, different types and so forth.

The Binary attachment component is handled in issue Altinn/altinn-studio#769 (Altinn Studio view) and Altinn/altinn-studio#291 (SBL)

**Sketch (if relevant)**
(Screenshot and link to Figma, make sure your sketch is public!)

**Navigation from/to (if relevant)**
This functionality is reached from...

**Technical considerations**
Input (beyond tasks) on how the user story should be solved can be put here.

**Acceptance criterea**
- What is allowed/not allowed
- Validations
- Error messages and warnings
- ...

**Tasks**
- [ ] Example task

No files, tests, or entry points are named. Start by reviewing the Binary attachment component work in Altinn/altinn-studio#769 and #291, then clarify thumbnail support and a consistent attachment view across types and services; done should be defined by concrete validations, allowed types, warnings, and acceptance criteria.

Written by the indexing model from the issue text.