Show persistent timestamps for operation and teacher messages

electron/coding-runtime/pi/runtime.ts

@@ -814,6 +814,7 @@ export class PiConversationRuntime implements CodingConversationRuntime {
         id: messageId,
         clientRequestId: input.clientRequestId,
         role: 'user',
+        timestamp: this.now(),
         status: 'optimistic',
         blocks: [
           ...(input.text.length > 0