feat(SEO): implement SEO configuration and meta tag management

- Added SEO defaults and route-specific configurations for improved search engine visibility.
- Introduced functions to normalize paths and retrieve SEO settings based on the current route.
- Enhanced server-side rendering to dynamically update meta tags for title, description, and robots directives.
- Created a utility for managing SEO-related meta and link tags in the frontend, ensuring consistent application of SEO practices across routes.
- Updated sitemap with new last modification dates and removed outdated entries for better search engine indexing.

frontend/index.html

@@ -13,6 +13,7 @@
     
     <title>Trainingstagebuch – Umfassende Vereinsverwaltung, Trainingsplanung & Turnierorganisation</title>
     <meta name="description" content="Das TrainingsTagebuch ist die umfassende Lösung für Vereine: Mitgliederverwaltung, Trainingsgruppen, Trainingszeiten, Trainingstagebuch, Turniere (intern, offen, offiziell), Team-Management, MyTischtennis-Integration, Statistiken, Berechtigungssystem – DSGVO‑konform und einfach zu bedienen." />
+    <meta name="robots" content="index,follow" />
     <link rel="canonical" href="https://tt-tagebuch.de/" />
 
     <!-- Open Graph -->