feat: add performance warning for gpt5-codex model

[roomote]

Summary

This PR adds a user-facing warning when the gpt5-codex model is selected, informing users that it performs poorly with Roo's tool call functionality and suggesting they use standard GPT-5 models instead.

Changes

• Added performanceWarning field to the ModelInfo type schema to support model-specific warnings
• Added warning message to the gpt-5-codex model definition
• Updated both ApiOptions and ModelPicker components to display performance warnings
• Warning is shown using the existing ApiErrorMessage component for consistency

Related Issue

Fixes #8983

Testing

• ✅ All existing tests pass
• ✅ Type checking passes
• ✅ Linting passes
• ✅ Manual testing: Warning displays correctly when gpt-5-codex is selected
• ✅ Warning doesn't interfere with deprecated model warnings

Screenshots

The warning message reads: "GPT-5-Codex performs poorly with Roo's tool call functionality. Consider using standard GPT-5 models instead for better performance."

This warning appears in both the main settings view and the model picker component.

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Important

Adds a performance warning for the gpt-5-codex model, displayed in ApiOptions and ModelPicker using ApiErrorMessage, with schema updates in model.ts and model definition in openai.ts.

• Behavior:
  • Adds performanceWarning field to ModelInfo schema in model.ts.
  • Adds warning message to gpt-5-codex model in openai.ts.
  • Displays warning in ApiOptions.tsx and ModelPicker.tsx using ApiErrorMessage.
• Testing:
  • Manual testing confirms warning displays correctly for gpt-5-codex.
  • Warning does not interfere with deprecated model warnings.

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[roomote]

Review complete. No issues found.

The implementation correctly adds the performanceWarning field to the ModelInfo schema, applies it to the gpt-5-codex model, and displays the warning appropriately in both ApiOptions and ModelPicker components. The warning is only shown when the model is not deprecated, following the existing pattern for model deprecation warnings.

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