fix(ui): use portable crypto API and async bootstrap pattern

fix(ui): use portable crypto API and async bootstrap pattern

- Replace node:crypto import with globalThis.crypto.randomUUID() in
  ui-common UUID utility for browser compatibility
- Rewrite ui-web main.ts with async bootstrap() pattern instead of
  top-level await, following Vue.js community best practices
- Remove unused ToastPlugin registration (all code uses useToast()
  composable directly)
- Add granular error handling for fetch, parse, and init phases