Config option to raise model reasoning effort silently ignored — hardcoded provider allowlist shadows it

A config setting meant to raise an agent's reasoning/thinking effort to the top tier (e.g. "xhigh") had NO effect — the model kept running at a clamped lower tier ("high"). Setting the per-model capability override in config (supportedReasoningEfforts including the high tier) also did nothing, and one attempt even broke the model's effort resolution entirely. The model itself supports the high tier (invoking the underlying CLI directly with the top-tier effort flag works fine), so the limit was purely in the framework's resolution layer.