refactor(dashboard,desktop,engine): remove unused imports, props, and locals

Clears the remaining no-unused-vars warnings across the dashboard app and
server, desktop main, and engine sources. Dead React state destructures are
collapsed to setter-only, unused props are underscore-prefixed to preserve
API shape, and unreferenced catch bindings are dropped. No behaviour change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/desktop/src/main.ts

@@ -12,7 +12,7 @@ import {
   type WindowState,
 } from "./native.js";
 import { setupTray } from "./tray.js";
-import { getRendererUrl, getRendererFilePath, IS_DEVELOPMENT, isUrlRenderer } from "./renderer.js";
+import { getRendererUrl, getRendererFilePath, isUrlRenderer } from "./renderer.js";
 
 // Re-export for backward compatibility
 export { IS_DEVELOPMENT } from "./renderer.js";