• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

I noticed Opus 4.6 already uses adaptive thinking in ProviderTransform.variants, but Sonnet 4.6 still falls back to type: "enabled" with budgetTokens.

Anthropic now recommends adaptive thinking for both Opus 4.6 and Sonnet 4.6, so it would be great to align Sonnet 4.6 with the same behavior.

Requested update:

• include Sonnet 4.6 in adaptive model detection
• return adaptive variants (low, medium, high, max) for Anthropic, Gateway, and Bedrock paths
• keep current manual budgetTokens behavior for other Anthropic models

I opened PR #14283 with this change plus tests.