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>

tests-ui/tests/platform/settings/components/SettingItem.test.ts

@@ -1,107 +0,0 @@
-import { flushPromises, shallowMount } from '@vue/test-utils'
-import { describe, expect, it, vi, beforeEach } from 'vitest'
-
-import SettingItem from '@/platform/settings/components/SettingItem.vue'
-import type { SettingParams } from '@/platform/settings/types'
-import { i18n } from '@/i18n'
-
-/**
- * Verifies that SettingItem emits telemetry when its value changes
- * and suppresses telemetry when the value remains the same.
- */
-const trackSettingChanged = vi.fn()
-vi.mock('@/platform/telemetry', () => ({
-  useTelemetry: vi.fn(() => ({
-    trackSettingChanged
-  }))
-}))
-
-const mockGet = vi.fn()
-const mockSet = vi.fn()
-vi.mock('@/platform/settings/settingStore', () => ({
-  useSettingStore: () => ({
-    get: mockGet,
-    set: mockSet
-  })
-}))
-
-/**
- * Minimal stub for FormItem that allows emitting `update:form-value`.
- */
-const FormItemUpdateStub = {
-  template: '<div />',
-  emits: ['update:form-value'],
-  props: ['id', 'item', 'formValue']
-}
-
-describe('SettingItem (telemetry UI tracking)', () => {
-  beforeEach(() => {
-    vi.clearAllMocks()
-  })
-
-  const mountComponent = (setting: SettingParams) => {
-    return shallowMount(SettingItem, {
-      global: {
-        plugins: [i18n],
-        stubs: {
-          FormItem: FormItemUpdateStub,
-          Tag: true
-        }
-      },
-      props: {
-        setting
-      }
-    })
-  }
-
-  it('tracks telemetry when value changes via UI (uses normalized value)', async () => {
-    const settingParams: SettingParams = {
-      id: 'main.sub.setting.name',
-      name: 'Telemetry Visible',
-      type: 'text',
-      defaultValue: 'default'
-    }
-
-    mockGet.mockReturnValueOnce('default').mockReturnValueOnce('normalized')
-    mockSet.mockResolvedValue(undefined)
-
-    const wrapper = mountComponent(settingParams)
-
-    const newValue = 'newvalue'
-    const formItem = wrapper.findComponent(FormItemUpdateStub)
-    formItem.vm.$emit('update:form-value', newValue)
-
-    await flushPromises()
-
-    expect(trackSettingChanged).toHaveBeenCalledTimes(1)
-    expect(trackSettingChanged).toHaveBeenCalledWith(
-      expect.objectContaining({
-        setting_id: 'main.sub.setting.name',
-        previous_value: 'default',
-        new_value: 'normalized'
-      })
-    )
-  })
-
-  it('does not track telemetry when normalized value does not change', async () => {
-    const settingParams: SettingParams = {
-      id: 'main.sub.setting.name',
-      name: 'Telemetry Visible',
-      type: 'text',
-      defaultValue: 'same'
-    }
-
-    mockGet.mockReturnValueOnce('same').mockReturnValueOnce('same')
-    mockSet.mockResolvedValue(undefined)
-
-    const wrapper = mountComponent(settingParams)
-
-    const unchangedValue = 'same'
-    const formItem = wrapper.findComponent(FormItemUpdateStub)
-    formItem.vm.$emit('update:form-value', unchangedValue)
-
-    await flushPromises()
-
-    expect(trackSettingChanged).not.toHaveBeenCalled()
-  })
-})