WWDC 2026: SAM3 iOS Model

[kevchengcodes]

Summary

This PR brings in the "lite" SAM3 model that was demonstrated as part of WWDC. It includes Python code for a custom export of SAM3, and Swift updates for image segmentation runtime execution.

User Experience

Please see the updated models/sam3/README.md. The uv run models/sam3/export.py command will default to using the "lite" SAM3 model, but passing the --full flag will export the vanilla model from Hugging Face.

Code Changes

• standalone models/sam3/export.py now calls into the coreai-models package, but with the same PEP723 requirements as before
• Python custom primitives and module definitions for SAM3
• Swift changes to run the new multi-function SAM3
• updated post-inference mask processing to use bilinear upsampling for smoother renders