epic: Provider Extension - Cortex.cpp

[0xSage]

Goal

• Jan integrates Cortex.cpp and has a bug-free transition to Cortex.cpp
• Planning: planning: Jan's path to cortex.cpp? #3690

Tasklist

• Eng Spec (copy over from planning: Jan's path to cortex.cpp? #3690, replace this post)

Previous Issues

• feat: Jan supports new Cortex's Model Folder and model.yaml architecture #3633