fix(ai): handle redacted_thinking blocks, skip interleaved beta for adaptive models, drop temperature with thinking

- Map redacted_thinking to ThinkingContent with redacted: true instead of
  adding a new content type. The opaque payload goes in thinkingSignature,
  thinking text is set to "[Reasoning redacted]" so it renders naturally
  everywhere. Cross-model transform drops redacted blocks.
- Skip interleaved-thinking-2025-05-14 beta header for Opus 4.6 / Sonnet 4.6
  where adaptive thinking makes it deprecated/redundant.
- Do not send temperature when thinkingEnabled is true (incompatible with
  both adaptive and budget-based thinking).

Based on #1665 by @tctev

packages/ai/src/providers/transform-messages.ts

@@ -39,6 +39,11 @@ export function transformMessages<TApi extends Api>(
 
 			const transformedContent = assistantMsg.content.flatMap((block) => {
 				if (block.type === "thinking") {
+					// Redacted thinking is opaque encrypted content, only valid for the same model.
+					// Drop it for cross-model to avoid API errors.
+					if (block.redacted) {
+						return isSameModel ? block : [];
+					}
 					// For same model: keep thinking blocks with signatures (needed for replay)
 					// even if the thinking text is empty (OpenAI encrypted reasoning)
 					if (isSameModel && block.thinkingSignature) return block;