feat(Sitemap, SEO): update sitemap generation and SEO configurations

- Enhanced update-sitemap.sh to generate a new sitemap structure with lastmod dates for additional URLs.
- Updated SEO configurations in server.js and seo.js to allow indexing for impressum and datenschutz pages.
- Introduced a list of noindex prefixes to manage SEO settings dynamically based on route paths.
- Added structured FAQ schema in index.html to improve search engine visibility and user engagement.

backend/server.js

@@ -111,15 +111,38 @@ const SEO_ROUTE_CONFIG = {
   '/impressum': {
     title: 'Impressum | Trainingstagebuch',
     description: 'Impressum von Trainingstagebuch.',
-    robots: 'noindex,follow',
+    robots: 'index,follow',
   },
   '/datenschutz': {
     title: 'Datenschutzerklärung | Trainingstagebuch',
     description: 'Datenschutzerklärung von Trainingstagebuch.',
-    robots: 'noindex,follow',
+    robots: 'index,follow',
   },
 };
 
+const SEO_NOINDEX_PREFIXES = [
+  '/createclub',
+  '/showclub',
+  '/members',
+  '/diary',
+  '/pending-approvals',
+  '/schedule',
+  '/tournaments',
+  '/tournament-participations',
+  '/training-stats',
+  '/club-settings',
+  '/predefined-activities',
+  '/mytischtennis-account',
+  '/clicktt-account',
+  '/team-management',
+  '/permissions',
+  '/logs',
+  '/clicktt',
+  '/member-transfer-settings',
+  '/personal-settings',
+  '/orders',
+];
+
 function normalizeSeoPath(pathname = '/') {
   if (!pathname || pathname === '') return '/';
   if (pathname === '/') return '/';
@@ -132,9 +155,16 @@ function getSeoConfigForPath(pathname = '/') {
     .filter((routePath) => routePath !== '/' && normalizedPath.startsWith(routePath))
     .sort((a, b) => b.length - a.length)[0];
 
-  return (matchedPrefix && SEO_ROUTE_CONFIG[matchedPrefix])
-    || SEO_ROUTE_CONFIG[normalizedPath]
-    || { ...SEO_DEFAULTS, robots: 'noindex,follow' };
+  const configuredSeo = (matchedPrefix && SEO_ROUTE_CONFIG[matchedPrefix]) || SEO_ROUTE_CONFIG[normalizedPath];
+  if (configuredSeo) {
+    return configuredSeo;
+  }
+
+  const shouldNoindex = SEO_NOINDEX_PREFIXES.some((routePath) => normalizedPath.startsWith(routePath));
+  return {
+    ...SEO_DEFAULTS,
+    robots: shouldNoindex ? 'noindex,follow' : SEO_DEFAULTS.robots
+  };
 }
 
 function escapeHtmlAttribute(value = '') {