Composer: gpt-oss-120b on Groq (low reasoning) first, DeepSeek with thinking disabled as fallback

Composer: route DeepSeek via :fastest first (measured 6-13s vs 12-17s pinned)

Surface friendly errors via gr.Error, optional cover_word on /generate, provider order

MiniMax-Music3-Jam: describe a song, MiniMax Music 3 sings it