add-model

Add support for a new model family to Halo — the EP (expert-parallel) wrapper, the Liger coverage spec, router-balancing choice, and vendoring (with a removal-on-merge policy). USER-INVOKED ONLY. Use when the user asks to "add a new model", "support <model> for EP/MoE", "vendor a model not in transformers", "wire up Liger for <model>", or extend the model roster (the families listed in agent-docs/models/README.md).…