Added multi_prompts input for Video Segmentation

[ZHI-A0]

This change adds multi-prompt input support for video segmentation, enabling multiple objects to be tracked in a single run. A new multi prompt mode accepts SAM3_MULTI_PROMPTS, converts each prompt region into per-object video prompts (points/boxes), and handles multiple boxes per object. The UI now shows the multi_prompts input when prompt_mode=multi, and multi_prompts input will auto-switch the node into multi mode.

[Jalen-Brunson]

This is a great change. I installed it from @ZHI-A0's git. +1 to merging this ASAP!

[Jalen-Brunson]

@ZHI-A0 There's a bug in the widget that adds 2 points for a right click (in Chrome). I asked Claude to fix it:
sam3_multiregion_widget.js

[ZHI-A0]

@ZHI-A0 There's a bug in the widget that adds 2 points for a right click (in Chrome). I asked Claude to fix it: sam3_multiregion_widget.js

Thanks for pointing this out. In the original multi-prompts controller, there are two overlapping right-click handlers. I’ve commented out one of them in this update to fix the bug.