chore: migrate tests from tests-ui/ to colocate with source files (#7811)

## Summary

Migrates all unit tests from `tests-ui/` to colocate with their source
files in `src/`, improving discoverability and maintainability.

## Changes

- **What**: Relocated all unit tests to be adjacent to the code they
test, following the `<source>.test.ts` naming convention
- **Config**: Updated `vitest.config.ts` to remove `tests-ui` include
pattern and `@tests-ui` alias
- **Docs**: Moved testing documentation to `docs/testing/` with updated
paths and patterns

## Review Focus

- Migration patterns documented in
`temp/plans/migrate-tests-ui-to-src.md`
- Tests use `@/` path aliases instead of relative imports
- Shared fixtures placed in `__fixtures__/` directories

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7811-chore-migrate-tests-from-tests-ui-to-colocate-with-source-files-2da6d73d36508147a4cce85365dee614)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

src/composables/queue/useResultGallery.test.ts

@@ -0,0 +1,103 @@
+import { describe, it, expect } from 'vitest'
+
+import { useResultGallery } from '@/composables/queue/useResultGallery'
+import type { JobListItem } from '@/composables/queue/useJobList'
+
+type PreviewLike = { url: string; supportsPreview: boolean }
+
+const createPreview = (url: string, supportsPreview = true): PreviewLike => ({
+  url,
+  supportsPreview
+})
+
+const createTask = (preview?: PreviewLike) => ({
+  previewOutput: preview
+})
+
+const createJobItem = (id: string, preview?: PreviewLike): JobListItem =>
+  ({
+    id,
+    title: `Job ${id}`,
+    meta: '',
+    state: 'completed',
+    showClear: false,
+    taskRef: preview ? { previewOutput: preview } : undefined
+  }) as JobListItem
+
+describe('useResultGallery', () => {
+  it('collects only previewable outputs and preserves their order', () => {
+    const previewable = [createPreview('p-1'), createPreview('p-2')]
+    const tasks = [
+      createTask(previewable[0]),
+      createTask({ url: 'skip-me', supportsPreview: false }),
+      createTask(previewable[1]),
+      createTask()
+    ]
+
+    const { galleryItems, galleryActiveIndex, onViewItem } = useResultGallery(
+      () => tasks
+    )
+
+    onViewItem(createJobItem('job-1', previewable[0]))
+
+    expect(galleryItems.value).toEqual(previewable)
+    expect(galleryActiveIndex.value).toBe(0)
+  })
+
+  it('does not change state when there are no previewable tasks', () => {
+    const { galleryItems, galleryActiveIndex, onViewItem } = useResultGallery(
+      () => []
+    )
+
+    onViewItem(createJobItem('job-missing'))
+
+    expect(galleryItems.value).toEqual([])
+    expect(galleryActiveIndex.value).toBe(-1)
+  })
+
+  it('activates the index that matches the viewed preview URL', () => {
+    const previewable = [
+      createPreview('p-1'),
+      createPreview('p-2'),
+      createPreview('p-3')
+    ]
+    const tasks = previewable.map((preview) => createTask(preview))
+
+    const { galleryItems, galleryActiveIndex, onViewItem } = useResultGallery(
+      () => tasks
+    )
+
+    onViewItem(createJobItem('job-2', createPreview('p-2')))
+
+    expect(galleryItems.value).toEqual(previewable)
+    expect(galleryActiveIndex.value).toBe(1)
+  })
+
+  it('defaults to the first entry when the clicked job lacks a preview', () => {
+    const previewable = [createPreview('p-1'), createPreview('p-2')]
+    const tasks = previewable.map((preview) => createTask(preview))
+
+    const { galleryItems, galleryActiveIndex, onViewItem } = useResultGallery(
+      () => tasks
+    )
+
+    onViewItem(createJobItem('job-no-preview'))
+
+    expect(galleryItems.value).toEqual(previewable)
+    expect(galleryActiveIndex.value).toBe(0)
+  })
+
+  it('defaults to the first entry when no gallery item matches the preview URL', () => {
+    const previewable = [createPreview('p-1'), createPreview('p-2')]
+    const tasks = previewable.map((preview) => createTask(preview))
+
+    const { galleryItems, galleryActiveIndex, onViewItem } = useResultGallery(
+      () => tasks
+    )
+
+    onViewItem(createJobItem('job-mismatch', createPreview('missing')))
+
+    expect(galleryItems.value).toEqual(previewable)
+    expect(galleryActiveIndex.value).toBe(0)
+  })
+})