[refactor] Rename ResultGallery to MediaLightbox and address code review (#10235)

## Summary
Address code review feedback from #10134 by renaming the component and
improving implementation quality.

## Changes
- Rename `ResultGallery` → `MediaLightbox` across all references
- Replace `useEventListener(window, 'keydown')` with `@keydown` on
dialog element
- Remove change detector tests (`renders close button`, `prevents
default on arrow keys`)
- Remove redundant `toBeVisible()` before Playwright click (implicit
wait)
- Update keyboard tests to dispatch on dialog element instead of
`window`
- Sort button icon sizes (`icon-sm`, `icon`, `icon-lg`)
- Wire zoom event to lightbox in `MediaAssetCard` story via
`context.args`
- Add standalone `MediaLightbox` Storybook story under
`Platform/Assets/`

Fixes #10134

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10235-refactor-Rename-ResultGallery-to-MediaLightbox-and-address-code-review-3276d73d365081299b42f682373a12f1)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Alexander Brown <drjkl@comfy.org>
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/tests/resultGallery.spec.ts

@@ -3,7 +3,7 @@ import { expect } from '@playwright/test'
 import type { ComfyPage } from '../fixtures/ComfyPage'
 import { comfyPageFixture as test } from '../fixtures/ComfyPage'
 
-test.describe('ResultGallery', { tag: ['@slow'] }, () => {
+test.describe('MediaLightbox', { tag: ['@slow'] }, () => {
   test.beforeEach(async ({ comfyPage }) => {
     await comfyPage.settings.setSetting('Comfy.UseNewMenu', 'Top')
     await comfyPage.settings.setSetting('Comfy.VueNodes.Enabled', true)
@@ -39,9 +39,7 @@ test.describe('ResultGallery', { tag: ['@slow'] }, () => {
 
     // Hover to reveal zoom button, then click it
     await assetCard.hover()
-    const zoomButton = assetCard.getByLabel('Zoom in')
-    await expect(zoomButton).toBeVisible()
-    await zoomButton.click()
+    await assetCard.getByLabel('Zoom in').click()
 
     const gallery = comfyPage.page.getByRole('dialog')
     await expect(gallery).toBeVisible()