feat(security): add built-in Public role for anonymous dashboard access (#36548)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

superset/views/utils.py

@@ -107,7 +107,7 @@ def sanitize_datasource_data(
 def bootstrap_user_data(user: User, include_perms: bool = False) -> dict[str, Any]:
     if user.is_anonymous:
         payload = {}
-        user.roles = (security_manager.find_role("Public"),)
+        user.roles = (security_manager.get_public_role(),)
     elif security_manager.is_guest_user(user):
         payload = {
             "username": user.username,