refactor(frontend): bring shared/ui and pages/public under the 4-file rule

Two directories had grown past the plan's ≤4 files per folder constraint:
shared/ui (5 primitives, and the kit keeps growing) and pages/public (5 pages,
counting auth/ as a subfolder).

Split shared/ui by concept — text-field/ and share-code/ each with their own
tests/ — and move PageTitle to shared/layout, where the rest of the page chrome
lives. Flat UI tests become per-component tests; the PageTitle test follows the
component. Move LoginPage and RegisterPage into the existing pages/public/auth/
beside the AuthSplit layout they both use.

No behaviour change: 83 tests, clean tsc build, 1 known oxlint warning.

frontend/src/shared/layout/tests/layout.test.tsx

@@ -1,10 +1,11 @@
-import { screen, within } from '@testing-library/react'
+import { render, screen, within } from '@testing-library/react'
 import userEvent from '@testing-library/user-event'
 import { getI18n } from 'react-i18next'
 import { afterEach, expect, test } from 'vitest'
 import { routes } from '../../../app/routes'
 import { renderApp } from '../../../test/render'
 import { json, mockFetch } from '../../../test/fetch'
+import { PageTitle } from '../PageTitle'
 
 afterEach(async () => {
   await getI18n().changeLanguage('ru')
@@ -103,3 +104,11 @@ test('footer carries the github link and the disclaimer', async () => {
   const gh = screen.getByRole('link', { name: 'GitHub' })
   expect(gh.getAttribute('href')).toMatch(/^https:\/\/github\.com\//)
 })
+
+test('page title renders one h1 with an optional lead', () => {
+  render(
+    <PageTitle lead="Короткое описание">Мои конфиги</PageTitle>,
+  )
+  expect(screen.getByRole('heading', { level: 1, name: 'Мои конфиги' })).toBeInTheDocument()
+  expect(screen.getByText('Короткое описание')).toBeInTheDocument()
+})

frontend/src/shared/ui/share-code/ShareCode.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react'
 import { useTranslation } from 'react-i18next'
-import { Button } from './Button'
+import { Button } from '../Button'
 
 export function ShareCode({ code, label }: { code: string; label?: string }) {
   const { t } = useTranslation('common')

frontend/src/shared/ui/share-code/tests/share-code.test.tsx

@@ -0,0 +1,14 @@
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { expect, test, vi } from 'vitest'
+import { ShareCode } from '../ShareCode'
+
+test('share code copies to clipboard and confirms', async () => {
+  const user = userEvent.setup()
+  const writeText = vi.spyOn(navigator.clipboard, 'writeText').mockResolvedValue()
+  render(<ShareCode code="7KQ3M9XA" />)
+  expect(screen.getByText('7KQ3M9XA')).toBeInTheDocument()
+  await user.click(screen.getByRole('button', { name: 'Скопировать' }))
+  expect(writeText).toHaveBeenCalledWith('7KQ3M9XA')
+  expect(await screen.findByText('Скопировано')).toBeInTheDocument()
+})

frontend/src/shared/ui/tests/ui.test.tsx

@@ -1,45 +0,0 @@
-import { render, screen } from '@testing-library/react'
-import userEvent from '@testing-library/user-event'
-import { expect, test, vi } from 'vitest'
-import { Button } from '../Button'
-import { PageTitle } from '../PageTitle'
-import { TextField } from '../TextField'
-import { ShareCode } from '../ShareCode'
-import { Notice } from '../Notice'
-
-test('busy button is disabled and announces busy', () => {
-  render(<Button busy>Сохранить</Button>)
-  const b = screen.getByRole('button', { name: 'Сохранить' })
-  expect(b).toBeDisabled()
-  expect(b).toHaveAttribute('aria-busy', 'true')
-})
-
-test('text field links label and error', () => {
-  render(<TextField label="Почта" error="Введи почту" />)
-  const input = screen.getByLabelText('Почта')
-  expect(input).toHaveAttribute('aria-invalid', 'true')
-  expect(input).toHaveAccessibleDescription('Введи почту')
-})
-
-test('share code copies to clipboard and confirms', async () => {
-  const user = userEvent.setup()
-  const writeText = vi.spyOn(navigator.clipboard, 'writeText').mockResolvedValue()
-  render(<ShareCode code="7KQ3M9XA" />)
-  expect(screen.getByText('7KQ3M9XA')).toBeInTheDocument()
-  await user.click(screen.getByRole('button', { name: 'Скопировать' }))
-  expect(writeText).toHaveBeenCalledWith('7KQ3M9XA')
-  expect(await screen.findByText('Скопировано')).toBeInTheDocument()
-})
-
-test('error notice is an alert', () => {
-  render(<Notice tone="error">Неверный код</Notice>)
-  expect(screen.getByRole('alert')).toHaveTextContent('Неверный код')
-})
-
-test('page title renders one h1 with an optional lead', () => {
-  render(
-    <PageTitle lead="Короткое описание">Мои конфиги</PageTitle>,
-  )
-  expect(screen.getByRole('heading', { level: 1, name: 'Мои конфиги' })).toBeInTheDocument()
-  expect(screen.getByText('Короткое описание')).toBeInTheDocument()
-})

frontend/src/shared/ui/text-field/tests/text-field.test.tsx

@@ -0,0 +1,24 @@
+import { render, screen } from '@testing-library/react'
+import { expect, test } from 'vitest'
+import { Button } from '../../Button'
+import { Notice } from '../../Notice'
+import { TextField } from '../TextField'
+
+test('busy button is disabled and announces busy', () => {
+  render(<Button busy>Сохранить</Button>)
+  const b = screen.getByRole('button', { name: 'Сохранить' })
+  expect(b).toBeDisabled()
+  expect(b).toHaveAttribute('aria-busy', 'true')
+})
+
+test('text field links label and error', () => {
+  render(<TextField label="Почта" error="Введи почту" />)
+  const input = screen.getByLabelText('Почта')
+  expect(input).toHaveAttribute('aria-invalid', 'true')
+  expect(input).toHaveAccessibleDescription('Введи почту')
+})
+
+test('error notice is an alert', () => {
+  render(<Notice tone="error">Неверный код</Notice>)
+  expect(screen.getByRole('alert')).toHaveTextContent('Неверный код')
+})