fix: use getModel() temperature as single source of truth in OpenAI handler

[roomote-v0]

Related GitHub Issue

Closes: #12142

Description

This PR attempts to address Issue #12142. Feedback and guidance are welcome.

Root cause: The OpenAiHandler.createMessage() computed temperature independently from getModel(), ignoring defaultTemperature from custom model info. When using the OpenAI Compatible provider with models like kimi-for-coding (which only accepts temperature: 0.6), Roo Code sent temperature: 0 (the hardcoded default), resulting in a 400 error.

Fix: Make getModelParams() the single source of truth for temperature across all code paths:

1. getModel() now detects deepseek reasoner models and passes DEEP_SEEK_DEFAULT_TEMPERATURE as defaultTemperature to getModelParams() (matching how openrouter.ts handles this).
2. createMessage() streaming path uses the temperature returned by getModel() instead of computing it separately.
3. createMessage() non-streaming path now includes temperature from getModel() (was previously missing entirely).
4. completePrompt() now includes temperature from getModel() (was previously missing).

Temperature priority is now consistent everywhere: user override > model defaultTemperature > provider default (0).

After this fix, users can set defaultTemperature: 0.6 in their custom model info for kimi-for-coding and it will be respected.

Test Procedure

• Added 5 new tests covering temperature handling:
  • defaultTemperature from custom model info is sent when no user temperature is set
  • User-set modelTemperature takes priority over defaultTemperature
  • Default of 0 when neither is set
  • Non-streaming path includes temperature
  • completePrompt() includes temperature
• Updated 3 existing tests to reflect temperature now being included in non-streaming and completePrompt paths
• All 53 tests pass, lint passes, type-check passes

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes.
• Documentation Impact: No documentation updates required (internal behavior fix).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

No documentation updates needed -- this is an internal bug fix that makes existing configuration options work as documented.

Interactively review PR in Roo Code Cloud