fix: align reasoning payload typing for #24991 (thanks @stakeswky)

src/agents/pi-embedded-payloads.ts

@@ -2,6 +2,7 @@ export type BlockReplyPayload = {
   text?: string;
   mediaUrls?: string[];
   audioAsVoice?: boolean;
+  isReasoning?: boolean;
   replyToId?: string;
   replyToTag?: boolean;
   replyToCurrent?: boolean;