Should GIFs files be allowed in the Annotate question type

### Expected Behaviour

I think we should discuss which way is better:
1) Leave it as it is and allow adding GIF files (but they won't be behaving like GIFs)
2) Block adding GIF files

### Observed Behaviour

It is possible to add GIF files in the Annotate, but it will be added as a normal image, without moving which might be confusing for the users

### Reproduction Steps

Steps:
1. Navigate to the Project: https://test.getodk.cloud/projects/720/forms/draw-annotation-signature/submissions
2. Click on the New Submission
3. In the Annotate image click on the Choose Image and select any GIF file
4. GIF will be added as a normal Image

### Environment

- Browser version: Firefox 153.0 (64-bit)
- OS: Windows 11
- Web Forms version: v1.0.0

### Additional Context

Start by locating the Annotate question type and its image-file handling, then reproduce the GIF behavior using the provided project and submission steps. The issue needs a decision between allowing GIFs as static images and blocking them; done means the chosen behavior is implemented and verified for GIF uploads.

Written by the indexing model from the issue text.