feat(web): add backend switcher and connection status

Split the login page into backend list and credentials, show connection status in the sidebar and top bar, and render dialogs in a portal.

web/display/vite.config.ts

@@ -6,7 +6,7 @@ import { defineConfig, loadEnv } from 'vite'
 //   BACKEND_URL=https://mo.oeo.one npm run dev:display
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, fileURLToPath(new URL('..', import.meta.url)), '')
-  const backend = (process.env.BACKEND_URL ?? env.BACKEND_URL ?? 'http://localhost:5000').replace(/\/+$/, '')
+  const backend = (process.env.BACKEND_URL ?? env.BACKEND_URL ?? 'http://localhost:29181').replace(/\/+$/, '')
   return {
     base: '/',
     plugins: [react()],