Replace map_thinking_to_reasoning_effort() with resolve_reasoning_effort()
that uses a two-tier priority system:
1. Explicit output_config.effort: low/medium/high map 1:1, max → xhigh
2. Fallback: thinking.type + budget_tokens thresholds (<4k → low,
4k-16k → medium, ≥16k → high, adaptive → high)
Both Chat Completions and Responses API paths share the same helper,
ensuring consistent mapping across all OpenAI-compatible endpoints.