test: migrate 13 component tests from VTU to VTL (Phase 1) (#10471)

## Summary

Migrate 13 component test files from @vue/test-utils to
@testing-library/vue as Phase 1 of incremental VTL adoption.

## Changes

- **What**: Rewrite 13 test files (88 tests) to use `render`/`screen`
queries, `userEvent` interactions, and `jest-dom` assertions. Add
`data-testid` attributes to 6 components for lint-clean icon/element
queries. Delete unused `src/utils/test-utils.ts`.
- **Dependencies**: `@testing-library/vue`,
`@testing-library/user-event`, `@testing-library/jest-dom` (installed in
Phase 0)

## Review Focus

- `data-testid` additions to component templates are minimal and
non-behavioral
- PrimeVue passthrough (`pt`) usage in UserAvatar.vue for icon testid
- 2 targeted `eslint-disable` in FormRadioGroup.test.ts where PrimeVue
places `aria-describedby` on wrapper div, not input

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10471-test-migrate-13-component-tests-from-VTU-to-VTL-Phase-1-32d6d73d36508159a33ffa285afb4c38)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>

docs/testing/README.md

@@ -29,7 +29,9 @@ The ComfyUI Frontend project uses **colocated tests** - test files are placed al
 Our tests use the following frameworks and libraries:
 
 - [Vitest](https://vitest.dev/) - Test runner and assertion library
-- [@vue/test-utils](https://test-utils.vuejs.org/) - Vue component testing utilities
+- [@testing-library/vue](https://testing-library.com/docs/vue-testing-library/intro/) - Preferred for user-centric component testing
+- [@testing-library/user-event](https://testing-library.com/docs/user-event/intro/) - Realistic user interaction simulation
+- [@vue/test-utils](https://test-utils.vuejs.org/) - Vue component testing utilities (also accepted)
 - [Pinia](https://pinia.vuejs.org/cookbook/testing.html) - For store testing
 
 ## Getting Started