Add post-login welcome and friendly how-it-works guide

backend/app/routers/site.py

@@ -1,4 +1,5 @@
 from typing import Any, Dict
+from urllib.parse import urlsplit
 
 from fastapi import APIRouter, Depends
 
@@ -36,6 +37,13 @@ def _build_site_info(include_changelog: bool) -> Dict[str, Any]:
     }
     if include_changelog:
         info["changelog"] = (CHANGELOG or "").strip()
+        playback_url = (runtime.jellyfin_public_url or "").strip()
+        try:
+            parsed = urlsplit(playback_url)
+            valid = parsed.scheme in {"http", "https"} and bool(parsed.hostname) and not parsed.username and not parsed.password
+        except ValueError:
+            valid = False
+        info["mediaServerUrl"] = playback_url if valid else None
     return info