[Feature] Temporal Mask for Minimax Image to Video

### Feature Idea

Hello!

At this time Minimax image2video accepts only first frame and last frame, but there is no mechanism for insertion of multiple keyframes, because an option to make a temporal mask is missing. Multiple keyframes would be very helpful.

Can you look into this?

Thanks!

### Existing Solutions

_No response_

### Other

_No response_

The issue does not name files, tests, or an entry point. Start by locating the Minimax image-to-video implementation and tracing how first and last frames are passed; then determine the required temporal-mask behavior and how multiple keyframes should be represented and validated.

Written by the indexing model from the issue text.