Flag to end users in-line that files previously attached are no longer there when resuming a form

## Context

Part of action items for [2026-09-02-file-attachments-not-included-in-form-submission](https://docs.google.com/document/d/1_ZQdO6sa2IobYK4gaEptT2k45gUJHU7mh4nj5vK77QI/edit?tab=t.0)

When saving and resuming a form with files previously attached, currently files are removed on save and removed on resume. We have a warning in place, but **HMW make this harder to miss?**

- [ ] Decide how to flag to users in-line that files were not uploaded (especially if these fields are marked as optional) clearer that these have been “nulled” out.
- [ ] Placeholder / Warning that files were previously there – stronger emphasis in pop-up or in-line prompt
- [ ] Hide/flag file name from saved answers HTML so that it’s less confusing that the files aren’t included.
- [ ] Revisit and clarify warnings shown when saving, viewing, and resuming answers with file uploads ex: more emphasis with a styled warning alert
- [ ] If file inputs are not required, cannot wipe fully if we want to signal to end users, there might be value in guiding users through this with placeholders / warnings
- [ ] Consider something like keyword like email+freshdesk does for attachments if none are part of it?
- [ ] In-line indicator within the form/pop-up right before publishing that flags there’s file attachment in the form

## Screenshots

### When saving form answers / progress

### When viewing saved answers / HTML

### When resuming a form / loading answers

### When downloading a copy of submission / on confirmation page

The issue names no files or tests. Start by reproducing the save, view, resume, download, and confirmation flows shown in the screenshots, then trace the existing file-upload warnings in the form UI. Done requires an agreed and implemented inline indication that previously attached files are unavailable across the affected flows, with updated tests.

Written by the indexing model from the issue text.