fix(frontend): revert useChatSession mutation call to match generated API

The generated mutateAsync requires an argument even for void mutations
due to react-query typing. Use `as never` cast to satisfy both the
generated type and the void constraint.

autogpt_platform/frontend/src/app/(platform)/copilot/useChatSession.ts

@@ -95,7 +95,7 @@ export function useChatSession() {
   async function createSession() {
     if (sessionId) return sessionId;
     try {
-      const response = await createSessionMutation();
+      const response = await createSessionMutation({ data: null } as never);
       if (response.status !== 200 || !response.data?.id) {
         const error = new Error("Failed to create session");
         Sentry.captureException(error, {