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/hooks/useHelpShortcut.ts

@@ -0,0 +1,22 @@
+import { useEffect } from 'react'
+import { useHelpStore } from '../store/helpStore'
+
+/**
+ * `Escape` closes the help dialog (the lightbox first, when one is open). The
+ * `?` in the navbar is the only way in: a hotkey would fire while someone is
+ * typing a question mark into a note, and the help is one click away anyway.
+ */
+export function useHelpShortcut(): void {
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key !== 'Escape' || e.defaultPrevented) return
+      const { open, closeHelp, lightbox, openLightbox } = useHelpStore.getState()
+      if (!open) return
+      if (lightbox) openLightbox(null)
+      // A modal the reader opened while following a guide keeps its own Escape.
+      else if (!document.querySelector('.trek-modal-backdrop')) closeHelp()
+    }
+    window.addEventListener('keydown', onKey)
+    return () => window.removeEventListener('keydown', onKey)
+  }, [])
+}