Update AGENTS.md with electron packaging docs

AGENTS.md

@@ -71,6 +71,20 @@ npm install --omit=dev
 npm run start
 ```
 
+## Electron single-exe distribution
+To package as a single portable exe with built-in server:
+```bash
+cd web/electron
+npx electron-builder --win --x64
+```
+Output: `web/electron/release/OpenChamber.exe` (single portable exe, ~260MB)
+
+The exe includes:
+- Bundled Node.js runtime
+- Server code, static files, and CLI
+- System tray icon with context menu
+- Auto-starts server on port 3000
+
 ## Runtime entry points
 - Web bootstrap: `web/src/main.tsx`
 - Web server: `web/server/index.js`