refactor: Remove init_token handling from admin initialization logic and related tests

frontend/src/core/auth/types.ts

@@ -40,7 +40,6 @@ const AUTH_ERROR_CODES = [
   "provider_not_found",
   "not_authenticated",
   "system_already_initialized",
-  "invalid_init_token",
 ] as const;
 
 export type AuthErrorCode = (typeof AUTH_ERROR_CODES)[number];

frontend/src/core/threads/hooks.ts

@@ -322,7 +322,7 @@ export function useThreadStream({
   useEffect(() => {
     if (
       optimisticMessages.length > 0 &&
-      thread.messages.length > prevMsgCountRef.current
+      thread.messages.length > prevMsgCountRef.current + 1
     ) {
       setOptimisticMessages([]);
     }