TTS: Fix polling validation error

[vprashrex]

Is your feature request related to a problem?
Polling the GET /llm/call/{job_id} for a completed TTS job results in a 500 error with a pydantic validation issue instead of returning the job result. This failure disrupts the workflow and makes it difficult to access the generated audio content.

Describe the solution you'd like

• Fix the pydantic validation error causing the 500 response.
• Ensure that polling returns the completed job result with audio content accessible via a presigned URL.

Original issue

Describe the bug
A clear and concise description of what the bug is.
Polling GET /llm/call/{job_id} for a completed audio (TTS) job returns a 500 with a pydantic validation error instead of the job result.

To Reproduce
Steps to reproduce the behavior:

1. Create an LLM job with a TTS completion config (no callback URL)
2. Wait for job to complete (status: SUCCESS)
3. Poll GET /llm/call/{job_id}
4. Receive 500 error instead of the job result

Expected behavior
A clear and concise description of what you expected to happen.
Polling returns the completed job result with audio content accessible via a presigned URL (format: "url").

Screenshots
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Additional context
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