feat(SEO): update meta tags and structured data for improved search visibility

- Revised title and description meta tags in index.html for better alignment with the application's focus on table tennis club management.
- Updated Open Graph and Twitter meta tags to reflect the new branding and features of the application.
- Enhanced structured data implementation in SeoLandingPage.vue to support JSON-LD for better SEO performance.
- Adjusted sitemap.xml to reflect updated last modified dates for improved indexing.
- Refined content in ClubMemberManagementPage.vue to emphasize member profiles and data management.

frontend/public/sitemap.xml

@@ -5,43 +5,43 @@
         http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
   <url>
     <loc>https://tt-tagebuch.de/</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>weekly</changefreq>
     <priority>1.0</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/impressum</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>yearly</changefreq>
     <priority>0.3</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/vereinssoftware-tischtennis</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/mitgliederverwaltung-verein</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/trainingsplanung-tischtennis</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/turniersoftware-tischtennis</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>monthly</changefreq>
     <priority>0.8</priority>
   </url>
   <url>
     <loc>https://tt-tagebuch.de/datenschutz</loc>
-    <lastmod>2026-03-27</lastmod>
+    <lastmod>2026-04-01</lastmod>
     <changefreq>yearly</changefreq>
     <priority>0.3</priority>
   </url>