sync: add fish audio provider

[Copilot]

The upstream Docs repo added fish.json (Fish music generation) as an audio provider, with endpoints /fish/audios, /fish/voices, and /fish/tasks. It was missing from both SDK implementations.

Changes

• TypeScript (resources/audio.ts): Added 'fish' to AudioProvider union type
• TypeScript (resources/tasks.ts): Added fish: '/fish/tasks' to SERVICE_TASK_ENDPOINTS
• Python (resources/audio.py): Added "fish" to AudioProvider Literal
• READMEs: Updated audio provider tables in both typescript/ and python/

Usage

await client.audio.generate({ prompt: 'A folk song', provider: 'fish' });

client.audio.generate(prompt="A folk song", provider="fish")