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/useScreenRoute.ts

@@ -0,0 +1,14 @@
+import { useLocation } from 'react-router'
+
+/**
+ * A screen's route ready to follow. A trip screen's route carries `:id`, which
+ * only the address of the trip the reader is on can fill in; browsed from
+ * elsewhere, such a screen has no way in and the button stays away.
+ */
+export function useScreenRoute(route: string | undefined): string | null {
+  const { pathname } = useLocation()
+  if (!route) return null
+  if (!route.includes(':id')) return route
+  const match = /^\/trips\/(\d+)/.exec(pathname)
+  return match ? route.replace(':id', match[1]) : null
+}