New tool supporting MiniMax music generation, ElevenLabs sound effects,
and Suno music (stub). Registers Suno as a valid provider type.
- create_audio.go: tool definition with provider chain for music, direct ElevenLabs for SFX
- create_audio_minimax.go: MiniMax music API (/music_generation)
- create_audio_elevenlabs.go: ElevenLabs sound effects API (/v1/sound-generation)
- create_audio_suno.go: stub for future Suno integration
- Add ProviderSuno type to store and gateway registration