test(04-01): add playlist flow E2E tests

- Test playlist list display
- Test playlist selection and execution
- Test navigation between browse and playlists pages

frontend/e2e/playlist-flow.spec.ts

@@ -0,0 +1,56 @@
+import { test, expect } from '@playwright/test'
+import { setupApiMocks, resetMockStatus, getMockStatus } from './mocks/api'
+
+test.describe('Playlist Flow E2E', () => {
+  test.beforeEach(async ({ page }) => {
+    resetMockStatus()
+    await setupApiMocks(page)
+  })
+
+  test('navigates to playlists page and displays playlists', async ({ page }) => {
+    await page.goto('/playlists')
+
+    // Wait for playlists to load
+    await expect(page.getByText('default')).toBeVisible()
+    await expect(page.getByText('favorites')).toBeVisible()
+  })
+
+  test('can select and run a playlist', async ({ page }) => {
+    await page.goto('/playlists')
+
+    // Wait for playlists
+    await expect(page.getByText('default')).toBeVisible()
+
+    // Click playlist to select
+    await page.getByText('default').click()
+
+    // Wait for selection
+    await page.waitForTimeout(500)
+
+    // Find and click run button
+    const runButton = page.getByRole('button', { name: /run|play|start/i }).first()
+    await expect(runButton).toBeVisible()
+    await runButton.click()
+
+    // Verify playlist is running
+    await page.waitForTimeout(500)
+    const status = getMockStatus()
+    expect(status.is_running).toBe(true)
+    expect(status.playlist_mode).toBe(true)
+    expect(status.playlist_name).toBe('default')
+  })
+
+  test('can navigate between browse and playlists', async ({ page }) => {
+    // Start on browse
+    await page.goto('/')
+    await expect(page.getByText('star.thr')).toBeVisible()
+
+    // Navigate to playlists via nav
+    await page.getByRole('link', { name: /playlists/i }).click()
+    await expect(page.getByText('default')).toBeVisible()
+
+    // Navigate back to browse
+    await page.getByRole('link', { name: /browse/i }).click()
+    await expect(page.getByText('star.thr')).toBeVisible()
+  })
+})