docs: add app icon and demo image to readme (#8)

* docs: add app icon and demo image to readme

* docs: add readme demo image asset

Author: jacobjmc

OpenCodeMonitorDemo.png

@@ -1,3 +1,7 @@
+<p align="center">
+  <img src="public/app-icon.png" alt="OpenCode Monitor icon" width="128" height="128">
+</p>
+
 # OpenCode Monitor
 
 OpenCode Monitor is a desktop app for monitoring and interacting with [OpenCode](https://github.com/anomalyco/opencode) agents across multiple workspaces.
@@ -6,6 +10,8 @@ It is forked from [CodexMonitor](https://github.com/Dimillian/CodexMonitor) by D
 
 OpenCode Monitor is an independent community project and is not affiliated with or endorsed by the OpenCode team.
 
+![OpenCode Monitor demo](OpenCodeMonitorDemo.png)
+
 ## Status
 
 **Active development** — core REST/SSE support is live for thread/session lifecycle, event translation, messaging, model discovery, approvals, and image attachments. Remaining work is parity polish and OpenCode-specific UX cleanup.