feat(help): in-app help center with per-screen guides and pictures

A help icon on every screen opens a panel with the screen's overview, its
sub-screens, task guides with a framed picture per step, search across guides
and the wiki, and a switch to any other screen's help. Guides exist for the
dashboard, Vacay, Atlas, Collections, Journey (list, journal, studio), Settings
(all tabs), Admin (all tabs) and the trip frame; the trip's own screens are
in progress. Pictures are produced by Playwright (client/e2e/help), texts in
all 23 languages.

client/src/components/Help/HelpGuideView.test.tsx

@@ -0,0 +1,30 @@
+import React from 'react'
+import { describe, it, expect, beforeEach } from 'vitest'
+import { render, screen, fireEvent } from '../../../tests/helpers/render'
+import { useHelpStore } from '../../store/helpStore'
+import { getHelpGuide } from '../../help/registry'
+import HelpGuideView from './HelpGuideView'
+
+const initial = useHelpStore.getState()
+
+beforeEach(() => {
+  useHelpStore.setState(initial, true)
+})
+
+describe('HelpGuideView: links', () => {
+  it('offers the in-app link of a guide that has one and closes the dialog on the way', () => {
+    useHelpStore.setState({ open: true })
+    render(<HelpGuideView guide={getHelpGuide('widgets')!} />)
+    const link = screen.getByRole('link', { name: /Open Appearance settings/ })
+    expect(link).toHaveAttribute('href', '/settings?tab=appearance')
+    fireEvent.click(link)
+    expect(useHelpStore.getState().open).toBe(false)
+  })
+
+  it('lists every step and has no link for a quick guide', () => {
+    render(<HelpGuideView guide={getHelpGuide('delete-trip')!} />)
+    expect(screen.getAllByLabelText(/^Step \d$/)).toHaveLength(getHelpGuide('delete-trip')!.steps)
+    expect(screen.queryByRole('link', { name: /Open Appearance settings/ })).toBeNull()
+    expect(screen.getByRole('link', { name: /Open in Help & Docs/ })).toHaveAttribute('href', '/help/My-Trips-Dashboard#per-trip-actions')
+  })
+})