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.

server/src/nest/help/help.controller.ts

@@ -1,4 +1,4 @@
-import { Controller, Get, Param, Req, Res } from '@nestjs/common';
+import { Controller, Get, HttpException, Param, Query, Req, Res } from '@nestjs/common';
 import type { Request, Response } from 'express';
 import { Public } from '../auth/public.decorator';
 import {
@@ -6,11 +6,16 @@ import {
   getWikiPage,
   getWikiAsset,
   isLocalWiki,
+  searchWiki,
   WikiNotFound,
   type WikiPage,
   type WikiNavSection,
+  type WikiSearchHit,
 } from './wiki';
 
+/** Longest query the search accepts; anything past it is noise, not a question. */
+const SEARCH_MAX_QUERY = 120;
+
 /**
  * /api/help — embedded TREK wiki, served from the `wiki/` directory that ships
  * with the app (see wiki.ts for the GitHub fallback). Content is public docs,
@@ -25,6 +30,26 @@ export class HelpController {
     return getWikiIndex();
   }
 
+  /**
+   * Full-text search over the bundled pages, for the help panel's search box.
+   * `q` is required; `limit` is optional and clamped by the search itself.
+   */
+  @Get('search')
+  async search(@Query('q') q?: string, @Query('limit') limit?: string): Promise<{ hits: WikiSearchHit[] }> {
+    const query = (q ?? '').trim();
+    if (!query) throw new HttpException({ error: 'A search query is required' }, 400);
+    if (query.length > SEARCH_MAX_QUERY) {
+      throw new HttpException({ error: `Search query too long (max ${SEARCH_MAX_QUERY} chars)` }, 400);
+    }
+    const n = limit === undefined ? undefined : Number(limit);
+    if (n !== undefined && !Number.isInteger(n)) throw new HttpException({ error: 'limit must be an integer' }, 400);
+    try {
+      return { hits: await searchWiki(query, n) };
+    } catch {
+      throw new HttpException({ error: 'Help search unavailable' }, 502);
+    }
+  }
+
   @Get('page/:slug')
   async page(@Param('slug') slug: string, @Res() res: Response): Promise<void> {
     try {