Fix webhook notification by adding User-Agent header

Discord webhooks require a User-Agent header or they return 403 Forbidden.
Added 'Paper-Dynasty-Discord-Bot/1.0' as User-Agent.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

notify_restart.py

@@ -34,7 +34,10 @@ def send_restart_notification():
         req = urllib.request.Request(
             webhook_url,
             data=json.dumps(data).encode("utf-8"),
-            headers={"Content-Type": "application/json"},
+            headers={
+                "Content-Type": "application/json",
+                "User-Agent": "Paper-Dynasty-Discord-Bot/1.0",
+            },
         )
 
         response = urllib.request.urlopen(req, timeout=5)