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/Studio/StudioShell.tsx

@@ -20,6 +20,7 @@ import { TrimField } from './TrimField'
 import '../../styles/dashboard.css'
 import '../../styles/studio.css'
 import './bookFontFaces'
+import HelpButton from '../Help/HelpButton'
 
 /**
  * The Studio shell: top bar, page rail, workbench, inspector.
@@ -205,6 +206,8 @@ function StudioBar({
           <Download size={14} />
           <span className="st-tool-label">{s.t('journey.studio.export')}</span>
         </button>
+        {/* Studio has no navbar, so the help center's button rides on its own bar. */}
+        <HelpButton className="st-tool is-icon" />
       </div>
     </div>
   )