fix(users): add manager to the valid-role whitelist

'manager' has been a fully-functional role throughout the app —
notifications, operator assignment, dispute mediation — but was
missing from both the user creation/update whitelist and the SSO
auto-provisioning role list, so a manager account could never
actually be created.

backend/app/services/sso_service.py

@@ -202,7 +202,7 @@ def process_callback(db: Session, request_data: dict) -> User:
     )
 
     # Validate role
-    valid_roles = {"admin", "red_lead", "blue_lead", "red_tech", "blue_tech", "viewer"}
+    valid_roles = {"admin", "red_lead", "blue_lead", "red_tech", "blue_tech", "manager", "viewer"}
     if role not in valid_roles:
         log.warning("SSO: unknown role '%s' for user '%s', falling back to default", role, username)
         role = cfg.default_role or "viewer"