feat: add Muse Spark 1.2 and Muse Spark 1.2 Contributor models

Muse Spark 1.2 (Standard): 1M ctx, .25 input / /bin/bash.15 cached / .25 output per M
Muse Spark 1.2 Contributor: 1M ctx, /bin/bash.10 input / /bin/bash.002 cached / /bin/bash.20 output per M

Both coding-optimized for agentic workflows with reasoning, tool calling,
image input, and OpenAI Responses compatibility. Pricing published by Meta.
Retain Muse Spark 1.1 as free preview tier.