feat: add timestamp and message version to prompt (#944) (#959)

### Summary

This PR implements a timestamp feature for messages in the prompt
window, responding to feature request #944.

**What this does:**
- Prefixes each sent message with a timestamp and message version.
### Screenshot

<img width="530" height="116" alt="image"
src="https://github.com/user-attachments/assets/62a86890-b120-42dd-ab48-8eeb4515a292"
/>

---------

Co-authored-by: Will Chen <willchen90@gmail.com>
Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>

src/ipc/ipc_types.ts

@@ -67,6 +67,7 @@ export interface Message {
   approvalState?: "approved" | "rejected" | null;
   commitHash?: string | null;
   dbTimestamp?: string | null;
+  createdAt?: Date | string;
 }
 
 export interface Chat {