fix: do not enforce temperature of 0 for OpenAI compatible provider

[roomote-v0]

Related GitHub Issue

Closes: #12042

Description

This PR attempts to address Issue #12042. When using the OpenAI compatible provider without a custom temperature set, the handler was hardcoding temperature: 0 in the API request. This overrode whatever server-side default the provider may have configured.

Changes:

1. src/api/providers/openai.ts (createMessage) - Changed the temperature fallback from 0 to undefined for the non-DeepSeek case, so the field is omitted from the request when no custom temperature is set.

2. src/api/providers/openai.ts (getModel) - Changed defaultTemperature: 0 to defaultTemperature: undefined so getModelParams also returns undefined when no temperature source provides a value.

3. src/api/transform/model-params.ts - Updated the GetModelParamsOptions type to allow defaultTemperature to be number | undefined.

4. Tests updated - Updated the Azure AI Inference test expectation and added a new test case verifying that undefined defaultTemperature produces undefined temperature output.

Scope and safety:

• Only affects the OpenAiHandler used for "OpenAI Compatible" provider type
• OpenAiNativeHandler (actual OpenAI) is in a separate file and unaffected
• DeepSeekHandler extends OpenAiHandler but overrides createMessage with its own temperature handling
• Other providers each have their own temperature logic and are unaffected

Feedback and guidance are welcome.

Test Procedure

• Ran npx vitest run api/transform/__tests__/model-params.spec.ts - all 58 tests pass
• Ran npx vitest run api/providers/__tests__/openai.spec.ts - all 48 tests pass
• All lint and type checks pass via pre-push hooks

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue.
• Scope: Changes are focused on the linked issue.
• Self-Review: Performed a thorough self-review.
• Testing: Updated existing test and added new test for undefined temperature behavior.
• Documentation Impact: No documentation updates required.
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

This fix aligns with the intent of Issue #7187 which previously addressed a similar problem.

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