fix(computer): force process exit after demo completes

The Node.js process hung after demo succeeded because Obsidian child
processes kept it alive. Use SIGKILL + process.exit(0) to ensure clean exit.

Author: quanru

computer/electron-demo/demo.ts

@@ -151,13 +151,14 @@ function launchApp(
 
     console.log('Electron demo completed successfully!');
   } finally {
-    // Cleanup: kill the Obsidian process
+    // Cleanup: kill the Obsidian process tree and force exit
     if (child.pid) {
       try {
-        process.kill(-child.pid, 'SIGTERM');
+        process.kill(-child.pid, 'SIGKILL');
       } catch {
         // Process may have already exited
       }
     }
+    process.exit(0);
   }
 })();