feat(util): add helper to detect Claude thinking models

internal/util/claude_model.go

@@ -0,0 +1,10 @@
+package util
+
+import "strings"
+
+// IsClaudeThinkingModel checks if the model is a Claude thinking model
+// that requires the interleaved-thinking beta header.
+func IsClaudeThinkingModel(model string) bool {
+	lower := strings.ToLower(model)
+	return strings.Contains(lower, "claude") && strings.Contains(lower, "thinking")
+}