fix: Bedrock GPT-5.4 reasoning levels

[celia-oai]

Why

When using the Amazon Bedrock provider with openai.gpt-5.4-cmb, the model picker allowed xhigh because the CMB catalog entry was derived from the bundled gpt-5.4 reasoning metadata. Bedrock rejects that effort level, causing the request to fail before the turn can run:

{"error":{"code":"validation_error","message":"Failed to deserialize the JSON body into the target type: Invalid 'reasoning': Invalid 'effort': unknown variant `xhigh`, expected one of `high`, `low`, `medium`, `minimal` at line 1 column 77239","param":null,"type":"invalid_request_error"}}

What Changed

• Replace the runtime lookup of bundled gpt-5.4 metadata for openai.gpt-5.4-cmb with an explicit Bedrock CMB ModelInfo entry.
• Advertise only the Bedrock-supported CMB reasoning levels: minimal, low, medium, and high.
• Keep the existing GPT OSS Bedrock model metadata and reasoning levels unchanged.
• Add catalog coverage for the hardcoded CMB metadata and Bedrock-compatible reasoning level list.