SEO: SERP-Titel/Description fixen, OG/JSON-LD, robots & sitemap

- index.html: beschreibender Titel ohne Em-Dash, gekuerzte Meta-Description,
  Open-Graph/Twitter-Tags, Canonical, Organization-JSON-LD
- Em-Dashes aus allen Seitentiteln entfernt (techday, gamejam, impressum, datenschutz)
- gamejam.html: fehlende Meta-Description ergaenzt
- robots.txt + sitemap.xml neu, .txt/.xml MIME-Typen im Server

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server.js

@@ -114,7 +114,9 @@ const MIME = {
   ".jpeg": "image/jpeg",
   ".ico": "image/x-icon",
   ".json": "application/json; charset=utf-8",
-  ".woff2": "font/woff2"
+  ".woff2": "font/woff2",
+  ".txt": "text/plain; charset=utf-8",
+  ".xml": "application/xml; charset=utf-8"
 };
 
 /* ---------- Lead-Speicher vorbereiten ---------- */