Simplify Agent chat with inline attachments and separate thinking

shared/cloud-agents.ts

@@ -98,6 +98,7 @@ export interface CloudInterrupt {
 export interface CloudMessage {
   id: number; role: 'user' | 'assistant' | 'system'; content: string; request_id: string;
   run_id: string | null; created_at: string;
+  reasoning_content?: string;
 }
 export interface CloudHistory {
   thread_id: string; messages: CloudMessage[]; run: CloudRun | null; next_offset: number | null;